For a windows 7 user – that I recently installed Acrobat Reader 10.1 – reporting to me that email attachments that were PDF files were not opening in Acrobat Reader rather in Media Center – but showing as empty here is a solution.
The steps top change the pdf association under windows 7 were
Open control panel
Select default Programs ( if don’t see this change from view by category to view by small icons at the right hand side of control panel)
Select Associate a file type ….
Scroll down to pdf
Double click and when the “open with” dialog is displayed select adobe reader
Click on close bottom right
check in explorer or other application t that clicking on pdf does open Acrobat reader