Depends ok the DRM technology. The only PDF DRM I came across so far was using the horrible feature by adobe digital editions.

It can be removed by using calibre and an unofficial plugin called noDRM, which should work on Mac as well (didnt test it tho, I dont own a Mac. Worked fine on windows tho)

I found it a pain in the ass to remove amazon drm ebooks. What worked for one book suddenly didn't for the next.

Whenever possible I try to avoid them for that reason