FREQUENTLY
ASKED
QUESTIONS
ABOUT
ELECTRONIC
PUBLICATIONS
Maintained by Harvey Jeffries (Harvey@unc.edu).
Lasted Updated May 30, 1995.
WARNING!
This Document is Incomplete.
Maintained by Harvey Jeffries (Harvey@unc.edu).
Lasted Updated May 30, 1995.
WARNING!
This Document is Incomplete.
Documents are information that use one or more of the following elements for communication: type, graphics, photos, audio, or video [Ames93]. An electronic document exists in electronic format (that is, as bits on a computer disk, or as frequency pulses on a telephone line) as opposed to existing on paper. Electronic documenents can be distributed by electronic mail. This places major restrictions on the actual form of the electronic document (see MIME types question), but not its logical contents (e.g., graphics and even programs can be sent through e-mail).
The native format file for word processing (WP) programs on various personal computers are one form of electronic document. Users with the same WP program, the same fonts installed in their systems, and maybe even the same graphics applications programs can meaningfully exchange these electronic documents. By using their WP application they can "read" these documents or even turn them into paper documents by printing them from the word processing application, and thus achieve communication. While there are utility programs that "convert" say a Word Perfect 5.1 document to a Microsoft Word 6.0 document--in fact, Word 6.0 will open and convert a Word Perfect file using its own internal conversion, do we all want to use one kind of operating system with one set of applications and one, or even two, word processor? Clearly, no. So, if we wish to have truely useful electronic documents, there has to be some other solution other than all of us using the same word processor.
All computers and operating systems can read and write American Standard Code for Information Interchange (ASCII) text files. This is an internationally accepted standard for exchanging text information electronically. ASCII-coded files go through all e-mail systems and thus can be easily transmitted via the Internet to anywhere in the world. Unfortuately, ASCII files communicate only character keystrokes; they carry no font information, no formatting information other than line breaks, and can not show graphics. Is there some way to use ASCII-coded text files while at the same time having our fonts, format, and graphics too? Fortuately, yes!
A "Portable Document" allows cross-platform, device independent transmission of its information (fonts, format, color, graphics). When you pick up the phone, you don't ask what kind of phone the person on the other end is using. Phones communicate to other phones. When you create an electronic document, you shouldn't have to think about where it is going, or what applications or which fonts are being used. You should just be able to send it and share it [Ames93]. To achieve these characteristics a special Portable Document Format (PDF) is necessary as well as a method for treating the fonts used in the document. Finally, we should not have to change any of our environments, or alter our hardware, software, or network configurations to have portable documents.
Before I can answer questions about PDF documents, you need to know something about PostScript and PostScript files.
PostScript can be described as a page description language that allows the creation, viewing, and printing of digital graphics and type. It was created in 1984 by Adobe Systems Inc [Adobe85] and was first licensed to Apple for the Apple LaserWriter printer. The combination of Aldus---now Adobe---PageMaker software on the early Macs and the original Apple PostScript LaserWriter gave rise to the entire industry of desktop publishing. The PostScript language specification is an open standard [Adobe85, Adobe85b] and now many applications (on DOS-PC's, Windows, and UNIX platforms) create PostScript language output. Fortunately because PostScript is ASCII encoded a PostScript file produced on one platform can be moved to another platform and sent to a PostScript printer there to produce the same output it would have on the original platform---that is provided the second platform has the same fonts that were available on the creating platform.
For additional details about Adobe PostScript Products you can download a PDF Document about PostScript produced by Adobe. You will need at least the Adobe Acrobat Reader for your platform to view this document. This Reader is free from Adobe.
PostScript printers require internal computer hardware that implements a PostScript interperter (i.e., a program executes in the printer that "reads" the commands in the PostScript source file and then controls the output to the printer's image system. A few years ago, the power of the computer chip and the amount of RAM memory in a PostScript printer often equaled or exceed that in the user's personal computer attached to the printer. With continued and rapid advances in chip hardware, this is no longer the case, and a good PostScript printer can be obtained for less than $1800. Further, Adobe has made its official interpreter ROM software available to many printer manufactors (e.g., Hewlett-Packard) and thus PostScript printers are now in common use on PCs as well as Macs and Unix machines. PostScript is also used in high-end, high-resolution (e.g.,>1200 dpi) type setting machines and color printers. About 80% of all printed material in the U.S. is produced on PostScript-based machines.
PostScript "code" is written with ASCII characters (and english words) that describes how pixels are to be painted on a page or monitor screen. Because it is made up of ASCII characters, PostScript can be used to create a type of portable document, and in fact many PostScript files for manuals and highly technical or graphic intensive docments are found on the Internet. You download these as ASCII text files by direct Ethernet or by modem to your local computer. Then you copy this file to a local PostScript printer to produce a high quality paper copy of the document.
On the Macintosh and on PCs with MS-Windows, printing is a function of the operating system by means of "print drivers" that are common across all applications. On Macintosh and Windows platforms Adobe supplies very advanced print drivers that convert the operating system's internal image model's commands into PostScript for directly feeding to the printer or for creating a file of PostScript code as ASCII text.
A font is a complete collection of letters, figures, symbols, punctuation, and special characters in a particular typeface. A font describes a specific design of an alphabet at one size and one typeface.
In 1984 as part of PostScript, Adobe introduced digital fonts which are just specially encoded PostScript "mini-programs" for each character. The Type 1 fonts---also called "outline fonts"---are hinted to change their shape slightly as a function of font size requested. This is needed to improve legibility of the characters as they are scaled to different point sizes. The first Apple LaserWriter had 13 fonts built-in to the memory of the printer. These were:
Later versions of the LaserWriter Plus included 22 more built-in fonts (a total of 35 fonts); the additions were:
Adobe alone sells more than 2000 Type 1 fonts. Like PostScript itself, the Type 1 font specification is also openly published and therefore others also sell Type 1 fonts.
These other Type 1 fonts can be "downloaded" to the printer's memory as part of a PostScript job. Downloading means to use a program on the user's computer to copy the Type 1 font code into the memory of the PostScript printer---usually only for one print job. The newer operating systems have mostly automated the font downloading process and therefore now the user rarely has to manually download fonts to the printer.
If the user's system does not have a copy of a particular Type 1 font, then when the user tries to print a document that requests the font, the printer will substitute Courier (a fix spaced font) for the missing font. Most likely the requested font was proportionally spaced and thus the printed output will be "messed up." One solution to this potential problem is to include the Type 1 font code for each requested document font in the PostScript file, so that when the docuemnt is sent to the printer, the fonts are also downloaded. This solution has a side effect of greatly increasing the size of the PostScript file. Another solution is to use only built-in fonts (i.e., just the 35 fonts shown above) and thus no Type 1 fonts have to be included in the PostScript file or downloaded to the printer.
While PostScript printers have built-in outline fonts, the computer screen for MS-Windows or Macintosh computers also need a representation of the fonts in use, but screen resolution is much less than the 300 dpi or 600 dpi of the printer. In fact, the standard screen resolution is 72 dpi. These graphical interfaces usually use a "bitmap" font for character display. A bitmap font is a pattern of dots that closely resembles a character shape in a given typeface, point size, rotation, and resolution. Bitmapped characters cannot be scaled without appearing jagged. Outline fonts can create a different bitmap for size needed and thus appear much smoother. Bitmaps also require considerable storage space. Thus there is usually one bitmap font for each point size of the desired typeface, i.e., Times Roman at 10 point, Times Roman at 12 point, etc. This turns out to be a lot of bitmap font files and thus a lot of disk space to store all the sizes and variety of typefaces.
Adobe came up with another solution to the screen font problem. They produced an add-on to the operating system that is capable of producing a screen bitmap font "on the fly" as the system needs them. The system extension is call Adobe Type Manager or just ATM. ATM uses the PostScript outline font as the source of the font shape and the operation it performs is similar to what the PostScript interpreter in the printer does to create a higher resolution version of the character for the page. Thus the same Type 1 outline font is used for both the printer and the screen. Usually one additional auxiliary font file is needed per font to connect the outline font to the operating system. ATM is available for the Macintosh, MS-Windows, OS/2, and Unix.
Adobe has modified ATM and PostScript interperters slightly to use an extension on the Type 1 font format. This extension allows multimaster or MM fonts. These are a parameterized Type 1 font in which some font attributes are dynamically adjustable before rendering by ATM. For example, one parameter might be the face weight (light to Demi to Bold, etc.) and another might be the character width. Using MM fonts, only one Type 1 font description needs to be downloaded to the printer and when different fonts realizations are needed, only the parameters need to be specified in the PostScript file. The MM code in the printer then renders a new realization of the font in the printer.
Adobe now has several MM font families and more are being added all the time. Because MM fonts are new, none are built-in to PostScript printers and all have to be downloaded as part printing a document. At the present time, Windows/Mac print drivers also do not automatically download MM fonts when they ceate the PostScript files from Windows/Mac applications. If an MM font is missing, the PostScript printer will "crash", print an error message, and flush the print job. So users need to remember to manually download any MM Type 1 fonts that they might use in any documents.
In font substitution ATM uses two special MM fonts "Adobe Sans MM" and "Adobe Serif MM" and a special font characteristic data base file which provides font parameters for a very large variety of font families. When a document is viewed on the computer screen or is printed on a PostScript printer, ATM first checks to see if the user's system has the particular Type 1 font installed. If it is, then ATM uses the installed Type 1 font. If the requested font is not installed on the user's system, ATM looks up the font parameters in the font data base file and uses these with one of the special serif or san serif multimaster font files to produce a near replicate of the font. That is, the rendered font will have the same size, occupy the same space on the display and page, and have approximately the same weight. This temporary replicate font can be downloaded to a PostScript printer just like real Type 1 fonts. When the computer is shutdown, these temporary fonts are deleted.
The use of font substitution means that the user does not have to have all the fonts used by the document creator in order to view or print a document on his computer. This method works with any application program on the PC/Mac including standard word processing programs. Font substitution makes it possible for you to view or print a docuemnt created on another computer that may have used hundreds of fonts that you don't have.
Based on PostScript and on ATM with font substitution, Adobe has developed and published a Portable Document Format specification [Adobe93]. Like PostScript, the PDF specifications are open so that third-party developers can create and read PDF files using their own applications. Several developers have already started adding PDF creation features to their document production applications, e.g., FrameMaker can automatically create PDF Bookmarks (see below) when it prints to a PostScript file.
A PDF file describes a document of any length and page size, containing any combination of text, graphics and images, in black and white or color, in a device- and resolution-independent format. PDF is designed to replicate the appearance of pages with the same high fidelity as the PostScript language. While it uses the PostScript language to describe the visual (printable) elements of a document, PDF also describes information such as user annotations; hypertext links within the document, between different PDF files even on different parts of a network, or different URLs on the WWW; miniature ÒthumbnailÓ views of pages; and ÒbookmarksÓ such as tables of contents and indexes.
PDF also includes standard data compression techniques to encode the entire document---text, graphics, structure---as a smaller, 7-bit ASCII character set encoded file. This means that PDF files can be e-mailed anywhere in the world without any problems. The typical data compression is about a factor of five over the source document format. Because it relies on font substitution technology built-in to ATM, PDF files do not have to include font definitions in the PDF file itself, only the parameters needed by ATM for rendering unusual fonts, thus keeping the PDF file small.
As it did with the PostScript language, Adobe published the PDF specification as an open standard for use by software developers. Adobe and Netscape have agreed for example to incorporate the PDF format into the next release of Netscape, thus allowing Netscape to select a page from a PDF file, transmit it over the WWW and render it in the Netscape browser at the client end. This means anything that be represented in color PostScript can be sent and viewed on the Web.
PDF Readers are freely available from Adobe. If you are using the WWW you go to http://WWW.Adobe.com/Software.html and follow the instructions for your platform. If you want to use standard anonymous ftp the URL to the Adobe ftp site is ftp://ftp.adobe.com/pub/adobe/Applications/Acrobat/Macintosh/. You can also purchase the Acrobat CD Sampler for $14.95. This CD-ROM contains the Macintosh, Windows, DOS, and UNIX versions of the Reader along with 1000's of pages of PDF files including periodicals like "wired" and books such as Shakespeare's plays, cookbooks, and the King James Bible.
Yes. In most circumstances you merely print your MS Word document to the PDFWriter. This will certainly be satisfactory for text only files.
A second way to obtain a PDF file from your word processor is to print it to a file using the PostScript print driver for your system. That is, you can save the PostScript output in a file on your disk instead of sending it to the printer. In the Adobe Version 8 Print Drivers you can select this option in the pop-up print dialog box that appears when you select "print" in the "file" menu. This will create a rather large file on your disk that has PostScript code in it. (If you are curious about what PostScript looks like this file can be examined with an editor or by opening it as a text file with your word processor). To create a PDF file from the PostScript file you use the Acrobat Distiller program. One advantage from using the Distiller is that it will produce a much smaller PDF file than can the PDFWriter. This is due to limitations imposed on the PDFWriter because has to act as a print driver. The Distiller route should also be used when you are using Encapsulated PostScript File (EPSF) graphics in the Word document to obtain higher resolution graphics images in the PDF file. The PDFWriter will include in the PDF file only the on-screen or preview image from the Word file because it can not interpret the PostScript code that is associated with the EPSF file, but which Word itself does not use.
Windows You can do this
On a Mac you merely use the Chooser to select the PDFWriter as the printer. In Word 6.0, then choose File/Print SetUp. When you are ready to print use File/Print just as you would if you were printing to a LaserWriter.
PostScript®, is a trademark of Adobe Systems Incorporated ("adobe"), registered in the U.S. and elsewhere. PostScript can refer both to the PostScript language and to Adobe's implementation of its PostScript language interpreter. Any reference to "PostScript printers", "PostScript files", or "PostScript drivers" refer to printers, files, and driver programs written in or supporting the PostScript language.
Adobe, the Adobe logo, Acrobat, the Acrobat logo, Adobe Sans, Adobe Serif, Adobe Type Manager, ATM, Distiller are trademarks of Adobe Systems Incorporated.
This page created by
Send comments or questions to harvey@unc.edu
Last Updated May 30, 1995