The most desirable results for PDF (and, by extension, most file extensions) are 1) Information about a program that can read or write PDF files 2) Informatio

The most desirable results for PDF (and, by extension, most file extensions) are 1) Information about a program that can read or write PDF files 2) Information about the PDF format The fact that both are shown as the first two entries is desirable. And the fact that wikipedia rounds out the top 3 is great.