If you receive a processing error after trying to run the Checklist, check the following items:
1. Is the document in Read-Only format?

If so, save the document as a .docx file and try again (File > Save As)

2. Is the document in Compatibility mode?

If so, save the document as a .docx file and try again.

3. Is track changes on? If so, turn track changes off and try again (you can turn track changes back on after the Checklist has been processed).

4. Is the document protected from making changes? If so, turn this protection off and try again.

5. A PDF needs to be converted to a Word Document. You can do that by right-clicking on the document, selecting Open with, and then selecting the option for Microsoft Word.

6. If your Word Document is too big to process with Catalyst, you can do a few things to help. Microsoft shows a few examples on their support page here.