Files with the extension DOCM are document files of Microsoft Word as of version 2007. They correspond to the files with the extension docx, but can also contain macros or VBA scripts. This means they do not have to contain macros, unlike docx files.
The extension DOCM means Word Open XML Macro-Enabled Document. Word Open XML stands for the general format of Microsoft Word 2007.
In addition to texts and formatting instructions, a DOCM file also contains images, graphics and macros. The included macros or scripts may contain malicious code, so you should do a virus check before running it and always install the latest security updates for Microsoft Office.
Docm is an XML based file format (Office Open XML), which is not directly readable with older Word versions. For the 2000, 2003, and XP Office versions, however, this functionality can be pared using the Microsoft Office Compatibility Pack, with the result of reading a DOCM file not always 100% the same as the original.
A DOCM file consists of several XML files, which are automatically combined with the ZIP algorithm as an archive when they are saved. This saves space compared to the old doc format. Other benefits include better data integrity and easier data recovery in case of data loss.
The file extension can be easily changed in case of problems in docx, but a correct execution of the scripts and macros can be subject to restrictions.