Hi Davide,

> Can't find in the documentation what files format are allowed for import.

The formats supported for opening are listed under the command reference File > Open section, here:
http://moi3d.com/3.0/docs/moi_command_reference1.htm#open

Export formats are listed in the command reference File > Save As section, here:
http://moi3d.com/3.0/docs/moi_command_reference1.htm#saveas

There is also some information about exporting in the Introduction section of the help file here:
http://moi3d.com/3.0/docs/moi_introduction.htm#export

Hope this helps!

- Michael