Why would anyone want to search engine optimize(SEO) their PDF files? Well, if you had an eBook, brochure, product description or technical document in PDF format, you may wish to optimize these to pick up some extra search engine traffic.

With so many businesses - especially retailers - having access to PDFs full of product information, here are some thoughts on optimizing PDFs for search engine visibility.

1. All three major engines can crawl and index text-based PDFs. If you need proof, just do a search on each search engine with PDF in the query.

2. PDF optimization is similar to optimization for a regular content page. Try this: good use of keywords/phrases, appropriate headlines and sub-headlines, solid content that reads well to a human eye, etc. If the PDF will include images, a caption underneath each image would be a good idea, especially if the caption includes a targeted keyword/phrase. (Of course, don’t overdo it.)

3. The most important thing where PDFs and SEO is concerned is how the PDF is created. Don’t use Photoshop to make your PDF, because when you do that, you’re actually making a big image file, not a true PDF - and the spiders cannot crawl or "read" the text from that image file. The PDF should be created with a text-based program, like MS Word or Adobe InDesign, so that the final product is text-based and can be crawled.

4. It’s probably a good idea to use a keyword when naming the files, such as keyword.pdf. I haven’t done any serious investigation on what impact this has, but there is no harm in doing it. Plus it seems logical.

5. Pay attention to the version. While search engines do "read" and index PDFs, search engines’ capabilities tend to lag new versions of Acrobat. Although Acrobat 9 is out, for now you should save your PDFs as a previous version to ensure search engines can index the content.

Not only is saving PDFs at a lower version good for the search engines, it’s also good for users. Not everyone has the latest versions of Acrobat Reader. Accordingly, I’d recommend saving PDFs as version 1.6 (Acrobat 7) or lower. This way it will be good for search engines and most readers.

6. Optimize the file size for downloading. Don’t post a huge PDF for download. Not only is this annoying and unnecessary for site visitors, it’s also troublesome for the search engines. If it’s too big, the search engines may abandon the PDF before even getting access to its content. Using the full version of Acrobat, select Advanced>PDF Optimizer to "right-size" the document.

You may also want to enable the "Optimize for Fast Web View" option in the Preferences>General Settings panel. This allows the PDF to be "loaded" a page at a time, rather than waiting for the whole PDF to download. Depending on your version of Acrobat these might be in different places.

7. Influence meta descriptions for PDFs. For web pages, the meta description is what is displayed under the title in a search result. With PDFs, the search engines search the copy of the PDF and select something to display. While with PDFs you have less control of what is displayed as the description to the search result, you can still influence this. The best way to do this is to make sure that you have a good, optimized sentence or two near the start of your PDF. By optimized, it should have good key words that your website targets. If these sentences correspond to the search term used, it’s likely that these sentences are the ones that will be displayed as the description under the search result’s heading.