PDF Research The Portable Document Format...
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256K1. PDF - What It Is
The Portable Document Format is, quite simply, Adobe Systems successor to the Postscript page description language. To understand the evolutionary relationship between Postscript and PDF Adobe has published a comparison of the two formats titled "PostScript vs. PDF" by David Evans.
Beyond a mere revision to Postscript 1 or 2, PDF is a revamping of the way pages are described digitally. It's development is current with Postscript Level 3, not a replacement for it. PDF files are characterized by the following components:
- Simplified postscript code - there are graphic constructs contained within many postscript files that need to be rasterized in RIP devices, sometimes without success. The simplified code of PDF files reduces the complexity of these constructs.
- Embedded Type 1 and Truetype fonts (optional) - the type characters and instructions for kerning and manipulating fonts are placed inside the file so that the receiver of the file does not need the font to view or process it. Simple changes are also possible.
- "Pre-rasterized" and compressed bitmap and vector graphics. Compression is dramatic - roughly 25% of size for vector graphics (with NO degradation of image) and anywhere from .5% to 75% of size for bitmap graphics (depending on settings). All PDF files are scalable (800%) and printable on postscript and non-postscript printers.
- Forms and indexing features - Enables PDF to become the foundation for a complete Integrated Document Management system. Indexes can be made across many documents stored on servers.
- Sound and Quicktime files linkage- Makes Acrobat Exchange a complete presentation generator and driver.
- Enabled hypertext-like linking - Interactive links between pages and views across documents makes PDF a dynamic option to any other publishing alternative.
- Page Independence - Unlike with Postscript, PDF pages are described independent of one another within the same document. This has several advantages: pages of different dimensions can be combined into the same document, individual pages can be RIP processed without interpreting the entire document, and downloading documents can be "byte-served."
2. How is PDF different from Postscript?
As explained by Jim Meehan, one of the Authors of the PDF specifications at Adobe, a PostScript file is a "program", an actual application that is created, sent and then run inside the PostScript RIP (Raster Image Processor), and that a PDF file is more of an "object database". When a PostScript file (or PostScript application, more accurately) is run, the PostScript commands are interpreted and then rasterized into a bitmap and normally imaged to paper, film or plates. The objects that describe graphical elements and entities in PostScript are difficult to parse or otherwise find or extract. This is where we are today with PostScript. Moreover, If you want to make a simple edit, such as a spelling correction, you normally need to go back to the original application file that created it. Editing PostScript is not very straight forward. In the case of PDF, this simply is not the case. Using Adobe applications such as Exchange, one can make that spelling correction on all the popular computer platforms, and if Distiller was set up properly, without requiring you to have the fonts! (See Michael Jahn's Afterword to the book PDF Printing and Publishing).
Byte-serving is a terrific innovation exploits the page independence difference between PDF and Postscript. This is how Adobe describes "byte-serving."
What is Byteserving (page-at-a-time downloading)?"With page-at-a-time downloading (byte-serving), a Web server that is serving PDF content sends only the requested page of information to the user, not the entire PDF document. As an online reader of the PDF document (viewing in the Web browser window), you do not have to do anything to make this happen; it is communicated in the background between the Acrobat viewer and the Web server using the "Byte Range Retrieval Extension to HTTP" protocol. However, if the user would like the entire PDF document to continue downloading in the background while they view the first page of requested information, they (or the Network Administrator) would select the "Allow Background Download of Entire File" option in General Preferences of the Acrobat Reader."
This affects how documents are optimally designed for online publishing. If the first page has links to other pages, then those pages are also available for access while the document is downloading.
For byte-serving to work, four things must be at play:
- The document must be Saved As "Optimized" out of Exchange.
- The browser must be able to handle byteserving (Navigator or Internet Explorer 3.0 or above).
- The Reader must be set for Allow Background Download of Entire File, an option in General Preferences of the Acrobat Reader.
- The server hosting the document must be able to handle byteserving. Visit the Adobe site for a listing of Webservers that support Byteserving "natively" (out of the box).
- For Windows users - if you have recently upgraded to MS Internet Explorer 4.0, you need to update your system with the latest ActiveX Control for Adobe Acrobat in order to enable PDF Search highlighting and page-at-a-time downloading (byteserving) of multipage PDF files.
3. PDF Background and Pervasiveness
In an article titled "Why PDF is Everywhere" written for INFORM magazine (9/97), an imaging periodical sponsored by AIIM, author Tony McKinley (From Paper to Web) writes a clear-cut description of PDF and its place in the imaging and digital publishing field. Included is an interview with John Warnock, Co-Founder and CEO of Adobe Systems, Inc., concerning the impetus behind the rapid development of PDF. Tony also discusses: PDF in Document Management and Information Retrieval, Converting Paper - Acrobat Capture compared to OCR, and Comparing Web formats - HTML and PDF.
The U.S. Government is one of the first, a certainly most pervasive users of the PDF format. Read a 1996 report by Motorola recommending that all government proposals (2.2Mb 35 pages) be accepted in PDF format. This document contains excellent comparisons of formats accepted by various departments of the federal government - PDF outscores them all. It also contains features and benefits lists and a sampling of pages from Canvas, Project, XPress, Powerpoint, Illustrator, FrameMaker, Interleaf, Excel, and Fast Track all converted and compressed into PDF pages.
The Internal Revenue Service has decided to dramatically reduce their printing, mailing, and customer service overhead by making all tax forms available on-line in the PDF format.
The Associated Press has made the distribution of ads via PDF a very profitable business. AP AdSEND is an advertising distribution service that will take a PDF file of an advertisement and distribute it via the internet to any of 1,400 newspapers that receive the service.
One of the truly useful implementations of PDF is the free APPLY! 98 CD-Rom that is being distributed out of Burlington, MA. This single CD is an invaluable reference for High School students and their parents who are comparing colleges, trying to arrange financial aid, and filling out applications. The applicant fills out a personal data sheet and then chooses the applications he/she wants. It contains more than 600 college applications all saved as PDF files that can be filled out and printed from the installed Reader on your machine. Available for Windows and Macintosh.
4. Uses of PDF Files
The PDF file format takes Postscript and makes it applicable across a broad range of applications. We have highlighted eight primary uses here, but there are many additional functions and workflows that PDF files can be incorporated into that exploit its best features: portability, graphic integrity, page independence, compression, and platform universality:
5. PDF Case Studies
Adobe has developed a PDF Demonstration Site that shows the initiate how different websites can be configured for viewing PDF files within the page or frame, or simply for downloading for the Reader or Exchange.
Testimonials
On the internet is a listing of brief (one or two paragraphs) user testimonials.
Case Studies
There are also an amazing range of corporate case studies of successful implementations for Adobe Acrobat®. Some are specific to the needs of advertising agencies, major utilities, software companies, etc.They are stored as PDF files and can be printed out. They are particularly useful if you are trying to justify implementing similar programs within a specific environment.
Many of these case studies are also published on the Acrobat Reader 3.x CD-ROM through the Acrobat Cafe.
Sample Sites
The following PDF files can be found at Adobe's Details site: Acrobat brochures for the Mac, Windows, and UNIX, a paper dealing with PDF format and production printing, a fact sheet on PDF, specifications for PDF, and a background document about the PDF format.
The PDF Directory site of Adobe is home to a variety of PDF files that can be accessed from the webpages of many contributors from a vast array of backgrounds.
Automated Graphic Systems is a printing and repurposing company that produces a bimonthly 8-page color newsletter called Autograph that is distributed on the web as PDF files (about 1 Mb/issue). All issues are searchable using the Verity PDF search engine.
6. PDF "How-To" Instructions
How to use the various components of Acrobat to create and modify PDF files is where the "rubber hits the road" in this web site. We have tried to document as many techniques as we have tried or read about all in one frameset area.
In addition, we have included tips and techniques for using PDF in various ways with some sample documents included. Check out our "How To..." section (also accessible by clicking on the frame listing at left).
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