In both cases it reads as if your computer has got the file associations in the Windows registry mixed up. (It happens a lot!)
The chances are that you've got a few PDFs stored on your computer. (If you're not sure where, a search for *.pdf will find all of them. Alternatively simply find a PDF on the internet and save it to your hard drive). Once you've located a PDF on your hard drive, right-click on it and select 'Open with'. Even if you see your PDF-vieweing program (such as Adobe Reader, Foxit or SumatraPDF) listed, DON'T immediately click on it. Instead, select 'Choose program'. THEN select the program you want to use AND put a tick alongside 'Always use this program . . .'.
Then go through the same process again with a Word document. Hopefully things will then be OK.
An alternative way of fixing the PDF problem (particularly if you're currently using the bloated 'Adobe Reader') is to install a better viewing program, allowing it to become your default application for handling PDFs. I use Sumatra PDF:
http://blog.kowalczyk.info/software/sumatrapdf/free-pdf-reader.html