The "PDF" files require the (free) Acrobat reader.
Note for Netscape (or Mosaic Firefox) or IExplorer users: If you are using an old version of Acrobat, you might get a "garbage display" when you click on a PDF link - all horizontal lines with little or no text.
This seems to be solved with recent versions of the Acrobat Reader - so if you have trouble, try downloading the latest version (actually, 4.05 or later seem ok, although the best results seem to be obtained with the current version).
For the more technically-minded: it is possible to solve this problem with the older versions as well, if you do not use the browser plugin for PDF files, since there is a configuration problem with the browser plugin and Acrobat. One solution is to just download the file and save it to a folder of your choice (right-click on the link and then "Save Link/Target As"...), and then open it (double click on the filename in "My Computer") in the usual way with Acrobat and it ought to look - and print - just fine.
You can also disable the plugin entirely if you are using Acrobat 4 or higher. Here is how to do that (in version 7 for example).
1.Open Adobe Acrobat Reader 7 2.Select the "Edit" menu option 3.Select "Preferences" 4.Select "Internet" 5.Unselect (un-check) the Box "Display PDF in Browser" and then click on "OK" 6.Exit Adobe Acrobat Reader(With other versions, the steps are essentially the same.) When you click on a PDF file, you may be prompted to save or open in current location: if so, you may choose either one, but only the second choice ("Open this file from its current location") will actually automatically open the Acrobat reader with the file.
I have tried this and it seems to work (!) both for Firefox and for Explorer - what happens is that the plugin is disabled and instead the PDF file displays in a separate Acrobat window. This has the additional benefit that you can keep the Acrobat window around while you continue browsing.
Note that none of this is a problem with the Opera browser, nor with any browser that is configured to launch Acrobat in a separate window, rather than in the browser window like Firefox and IE do.
I have also been told that some files do not print correctly (minus signs missing) if Acrobat 3 is used, even though the file displays correctly on screen - the recommendation again is to use the current version of Acrobat (or at least 4 or greater).