DSLR with Macro Lens
Document copying is fairly simple but needs good light that does not produce glare and you need to keep the camera still (on a tripod.) It must be square on to the subject to avoid distortion. Get a two way spirit level that fits in the external flash shoe to check the levels of both camera and document.
Macro lenses preform well on flat plain subjects whereas many other normal lenses will bring in distortion or will not focus close enough.
A macro lens of 60 mm focal length or less is what you want.
Don't skimp on the tripod and head or you will defeat your object. Good sturdy tripods are not cheap but last a lifetime and you don't want to buy one more than once.