Combine multiple PDF's into single file

running OS 10.8.5 on Macbook, using Acrobat Pro. Used to happily "combine multple files into single PDF" but now, when I pull down the create menu, and selec that, Acrobat just "goes away".

Both the OS and Acrobat versions are current and recently updated. The hardware otherwise passes all its diagnostics and bheaves normally.

I'm new to the forum, any suggestions would be welcome...

thanks.