An rk file extension is associated with the WinRK and used for its archive files.
RK file extension - WinRK archive
What is rk file? How to open rk files?
File type specification:
The rk file extension is related to the WinRK, a commercial archive utility not available for free usage. It supports popular archive file types like Zip but it also uses its own non-popular RK archive format.
This rk 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.