To use the adapter, I found that it's easier to screw the adapter to the front of a lens first, then mount or dismount the assembly to a camera body. In the adapter instructions, Pentax does not mention how to mount.
To use a filter, it should be added between the lens and adapter. With a filter, the magnification will be slightly increased.
A filter size adapter can be used if you lens does not match the reverse adapter.
Definitely, lenses with non-PK mount can be used on the reverse adapter as long as you can screw the lens onto the reverse adapter.
Below are five sample images without cropping, taken by a Pentax K-x and SMC Pentax-M 50mm 1.4 prime lens.