I have Adobe Acrobat Pro X for Mac, version 10.1.`6. Suddenly I can no longer digitally sign documents, which I use regularly. What can I do?
As Acrobat X Pro is not compatible with macOS 10.1.6 , you may face issue using the product, please refer to the following link: Adobe Acrobat system requirements
You might try following steps:
1- Check for Updates, launch Acrobat>click Help>select Check for Updates
2- Repair installation, under Help menu>select Repair Acrobat Installation