Hi cmatt3 ,
Would like to inform you that Acrobat X pro is not compatible with MAC El Capitan , refer to this KB article - https://helpx.adobe.com/acrobat/kb/system-requirements-acrobat-family-products.html#main__ Adobe_Acrobat_X_Standard__Pro__Suite%20(10)
This could be the reason for such behavior .
Meanwhile please check whether that document should not be open in any other application . Also check after restarting the machine.