Google, which claims "the largest index of websites available on the World Wide Web and the industry's most advanced search technology," has added the ability to index and search files in the Adobe PDF file format. Currently, the Google index contains over 13 million PDF documents which can be returned as part of a user's Google search.

Most other major search engines have do not index PDF documents because they are more complex than the HTML documents that make up most of the World Wide Web.

This marks a significant advance in searching the "Invisible Web" - (the estimated 5 billion pages o finformation on the Internet that is not indexed by any search engine either because it is a complex format such as PDF or resides in private or proprietary databases).

Since many researchers and universities utilize the PDF format for papers, theses and other research results, the addition of PDF files to the Google index is a boon to students, teachers and all researchers in general.

Because the PDF format requires users to download the Adobe Acrobat Reader software (available as a FREE download by clicking here), Google clearly highlights any PDF document returned in a search with a [PDF] next to the returned item. For those who do not have the Acrobat Reader software, Google also offers a link to a text version of the document (with the formatting and special fonts removed)