The DRMK system driver (drmk.sys) is the Microsoft Kernel DRM Descrambler Filter that decrypts audio streams containing DRM-protected content.
It lives in C:\WINDOWS\system32\drivers
You may have copies of it on your system.
I found copies in
C:\WINDOWS\LastGood\System32\DRIVERS
C:\WINDOWS\system32\ReinstallBackups\0006\DriverFiles\i386
C:\WINDOWS\system32\ReinstallBackups\0015\DriverFiles\i386
If a core file like this has gone missing you may have other problems.