Adobe Acrobat Doesn't Open
If Adobe Acrobat open doesn't open, or if PDF files do not open when clicked, this may be due to a damaged registration file.
This has been observed with Acrobat X but may also apply to other versions.
To resolve, open an elevated command prompt and type (if using 64-bit Windows):
ren "C:\Program Files (x86)\Common Files\Adobe\Adobe PCD\cache\cache.db" cache.was
If using 32-bit Windows, type:
ren "C:\Program Files\Common Files\Adobe\Adobe PCD\cache\cache.db" cache.was
Upon opening Acrobat, it may prompt to log in to your Adobe account or re-enter the product key.
This is also known to occur 30 days after installing Acrobat X as part of a CS suite. In this situation, deactivate the entire suite using a product other than Acrobat (Help → Deactivate), then re-activate using a product other than Acrobat.