M2k file format is the file format for the qualitative data analysis software from MAXQDA.
There is not much information about the file format, but it is a MS Access compatible format. If you open the file in a hex editor you see "Standard Jet DB". You can also rename the .m2k file to .mdb then you can open it in MS Access. There is also a free reader application that can export the data in different formats, for example XML.