Section 36.3. Portable Document Format (PDF)

36.3. Portable Document Format (PDF)

PDF (Portable Document Format) is a technology developed by Adobe for sharing electronic documents. The remarkable thing about PDF files is that they preserve the fonts, colors, formatting, and graphics of the original source document. Ideally, a PDF document looks exactly the way it was designed, regardless of the platform, hardware, and software environment of the end user. It can be viewed on the screen or printed out to a high-quality hardcopy.

PDF existed before the Web, but the two make great partnersPDF is the ideal file format for sharing documents, and the Web provides a highly accessible network for distributing them. You can make any document into a PDF file and make it available from a web page. The advantage, of course, is that you have precise control over fonts and layout.

Forms, documentation, and any other materials that rely on specific formatting are good candidates for PDF files. For example, the IRS makes tax forms available for download in PDF format so taxpayers can print them out at home.

PDF files are not necessarily static. They can contain links to online material and other PDF files. With Adobe Acrobat, authors can even create interactive PDF forms that can be filled out, automatically updated, and submitted online. PDFs can also be dynamically generated based on user input.

With the control PDF offers over presentation, it's tempting to want to use it for all online material. It's important to understand that PDF is not a substitute for HTML and CSS, nor is it likely ever to be. But it is a powerful tool for sharing any sort of document electronically. It's like sending a piece of paper through the lines.

36.3.1. Viewing PDF Files

PDFs are viewed and printed via the freely available and widely distributed Acrobat Reader . Acrobat Reader is also available as a plug-in (called PDFViewer) or ActiveX control and is supported by all the popular browsers (Internet Explorer, Netscape, Firefox/Mozilla, Safari, Opera) on a variety of platforms including Windows, Mac, and Unix.

When a user clicks on a link to a PDF file from a web page, what happens depends on how the browser is configured. If the browser has the PDFViewer plug-in , the document displays right in the browser window; the plug-in adds a toolbar to the browser window for navigating through the PDF document. If the browser is configured to use Acrobat Reader as a helper application, the browser automatically launches the reader, and the PDF displays in the separate application window.

Without the Reader or plug-in, when a browser encounters a PDF file, it issues a prompt to install the plug-in, choose a helper application, or save the file to disk.

36.3.2. Creating PDF Files

Creating PDFs is easy. Because it is open source, support for PDF has been built into many document creation tools. For example, Microsoft Word allows authors to save as PDF from the Print dialog box. Macintosh OS X includes native support for PDF, so any document may be saved as a PDF from the Print dialog box. When you save the PDF, be sure that you give it the proper .pdf suffix.

36.3.2.1. Adobe Acrobat

The commercial application for creating PDF files is Adobe Acrobat, which is in Version 7 as of this writing. Acrobat gives publishers the greatest control over PDF creation, including the ability to make interactive PDFs, a single PDF from multiple documents, electronic signatures, and other advanced features that you don't get when simply printing to PDF.

When Acrobat is installed on a computer, PDFs can be created from within Adobe, Microsoft Office, and selected other applications at the click of a button. In non-Adobe applications, such as QuarkXPress, the document is printed to a PostScript file (choose File instead of Printer in the Print dialog box) and then converted to PDF using Acrobat Distiller, part of the Acrobat package.

Once the PDF file has been created, it can be opened in Acrobat for further fine-tuning and advanced settings. See the Adobe web site (www.adobe.com/products/acrobat/main.html) or the Acrobat documentation for more information on creating and fine-tuning PDF files.

36.3.2.2. Fast Web view

You may also choose to optimize the PDF for Fast Web view. This enables page-at-a-time delivery of long PDF documents. When PDFs are not optimized, the entire document needs to be downloaded before it can be viewed. Check with your server administrator to be sure that your server supports page-at-a-time downloading.

36.3.2.3. Alternatives to Acrobat

Acrobat is not your only option for creating PDFs. Because PDF is an open source technology, Adobe has opened the door to third-party developers who want to support the ability to save documents as PDFs.

The best place to look for PDF-related tools is PlanetPDF (www.planetpdf.com), the "home of the PDF community." They maintain the most comprehensive and up-to-date listing of PDF tools and services.

Online PDF Converters

There are online PDF conversion services that convert uploaded documents to PDF for a small fee or subscription. Adobe has its own conversion service called Create Adobe PDF Online that charges a monthly fee, but your first five conversions are free. It is available at createpdf.adobe.com. Even better, check out PDF Online (www.gohtm.com), where they convert many file formats to PDF for free.

These services may be a good alternative if you only need to create PDFs occasionally. If you plan to make PDFs part of your publishing process, Acrobat is a good investment because of the advanced features it offers.

36.3.3. Adding PDF Files to Web Pages

There are two basic ways of accessing a PDF file from a web page: linking to the file (or a specific page within it) and embedding it in the page like an image.

36.3.3.1. Linking to a PDF file

Creating a link to a PDF file is the same as linking to any other document. Just include the filename in the URL, as shown in this example:

 <a href="documentation.pdf">Link to documentation (PDF)</a> 

The PDF file resides on the server like any other media file. Most modern server software is preconfigured to recognize the PDF MIME type (type application/pdf, extension .pdf).

36.3.3.2. Tips for linking to PDF files

As for any large media file, it is good web design etiquette to provide some indication of what users will get when they click on a link to a PDF file. The file format itself can be shown with a small PDF icon, by writing out the name of the file with its .pdf suffix, or by identifying the file type next to the link in parentheses, e.g., "link (PDF)."

As a courtesy to your users, consider also including a link to the Acrobat Reader download site. As of this writing, the URL is www.adobe.com/products/acrobat/readermain.html.

36.3.3.3. Embedding a PDF file

PDF files may also be embedded in a web page like an image. The standards-compliant markup for embedding a PDF is:

 <object type="application/pdf" data="directions.pdf" width="450" height="600"> </object> 

Browsers that use the Netscape plug-in architecture may require the nonstandard embed element to display the PDF inline. The href attribute is added so multipage PDF files will open in the reader if the image is clicked. (In Internet Explorer, multipage PDFs are accessible inline using the embedded Acrobat Reader controls for paging through the file.)

It is common for web authors to combine object and embed elements to cover all the bases like this:

 <object type="application/pdf" data="directions.pdf" width="450" height="600">   <embed src="/books/4/439/1/html/2/directions.pdf" width="450" height="400" href="directions. pdf">     <noembed><a href="directions.pdf">Link to documentation (PDF)</a></ noembed>   </embed> </object> 

Be aware that embed is a nonstandard element that will prevent an (X)HTML document from validating. We are moving toward a standards-compliant Web in which the object element alone will be sufficient, but for the time being, the embed element is still being used to ensure cross-browser support of embedded media.