zmf seems to be the native format of
Zoner Draw, a czech drawing program. It's probably commercial sofware.
That file format is among the ones xnview
supposedly reads. My copy of xnview won't display pics when their names uses non latin characters (e.g. japanese kanji and kana and some other special characters). Try renaming the files in Windows Explorer if the names use diacritics?
Edit: OK,
found a link on the french language page to a download that doesn't ask for your e-mail. Evaluation copy or fully functional?