What is Pentax K+ Multi-Mount (PK+MM)?
PK+MM introduces a new method of adapting other camera mount lenses. As most camera mounts have flange focal distance that are too close for adapters to be possible, by changing the original mount ring of the camera to an adaptive one like PK+MM, you can now mount different mount lenses without adapters, yet achieving infinity focus in most cases. There is absolutely no degradation to image quality as there is no optical elements like other adapters.

Can Pentax K mount lenses still be used?
Yes, definitely. PK+MM is designed to accept other camera mount lenses in addition to its original K mount.