Why Avira Antivirus Caot Read some .chm Files?

Waing in Windows 10 Education edition

C:Usersmasidocument.chm [WARNING] The file could not be read!

I would like to understand why Avira caot read the file, documents are mostly .chm files. I can read them still in my system.

Why Avira Antivirus caot read some .chm files in your system?