Sharepoint has a limited number of icons available, specially for Office aplications, but you can add more icons if needed, like a PDF. There is an SPSIcons.zip file available in the web that has some icons that you can use to include in Sharepoint.
To do so you need to have:
– The icons have to have 16X16 pixels size
– Need to be placed in the …60/TEMPLATE/IMAGES folder,and rename it IC???.GIF (ICPDF.GIF in the case of PDF)
Note: Make a copy of the new icon and call it ???16.GIF(PDF16.GIF in the case of PDF), this new icon enables the new icon to be showned in the search results.
– Add an entry of the new icon file type in the DOCICON.XML, tou can find this file in …60/TEMPLATE/XML.
Finally you need to perform an IISRESET (Start -> Run -> cmd type iisreset on the command line).