When trying to download a file, such as a knitting pattern, I sometimes get a message with: pdf is not a valid win 32 application.
I also have to say that I'm not very computer literate. A little yes. A lot no.
Right-click the file in Windows Explorer, select "Open with.." Select "Choose Program"
Look for Acrobat in the list that shows, if it is there, select it and check the box to always open this type file with this program.
If Acrobat is not in the list... click the Browse button.
Browse to Program Files, Adobe, Acrobat5.0, Reader, and finally select the AcroRd32.exe file.
Check the box to always open this type file with this program.
You may have an Acrobat version higher than 5.0, but the process is still the same, only the version number will be different.
Here's a picture of what it looks like in your system drive... You will not see such an expanded view, you will see these items one folder level at a time as you proceed, but here is where you are going.
However, if you do not have Acrobat Reader in your computer you will need to download it and install it to view Pdf files.