A drvf file extension is related to the FaxSTF software. Probably obsolete software.
DRVF file extension - FaxSTF driver
What is drvf file? How to open drvf files?
File type specification:
The drvf file extension is associated with the FaxSTF a tool for Apple Mac OS X operating system that allows users to send and receive faxes from their computer.
The drvf file stores driver used by Smith Micro FaxSTF.
FaxSTF is obsolete product. The last version is available for OS X 10.5.
This drvf file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.