Why do some pdf files not open with Adobe Reader X, most open OK?

On my wife's 64 bit WIN 7 computer, a some pdf files will not open, but most open OK.
She uses Acrobat Reader X and MS Office 2010.

The same problem files open with no problem on my very similar computer.
Is the problem with some setting on the Acrobat Reader or something else?

Sometimes there is this error message when the problem files do not open:

Find Click2run64.msi file to install MS Office Click to Run.
But MS Office Click to Run is already installed on her PC.  It is not on my PC.

Thanks for your help.