Q: how do i open a .docm in microsoft word for mac?

I suggest you ask your question on the Microsoft Mac forums where the Office experts hang out, as these forums are for troubleshooting compatibility issues between Mac OS and Windows.

http://answers.microsoft.com/en-us/mac

In addition to Templeton Peck's advice

Some background on .docm

http://www.word-tips.com/docm/

It has Macros in it.

If you have Office you should be able to open it.  Or ask whoever created it to save it as .doc or .docx and send it to you.

As Sparkleberry mentioned, a .docm has VBA macros in it. If you using Word 2016 for Mac, you may have problems opening a iy because it has only partial support for the VBA program language at this time.