I don't think you'd be able to get paper in there even if they're 100% right/normal. MAYBE a 0.001" or 0.002" feeler gauge, but paper is thicker than that.
Is it HARD to spin the wheel? If so, crack a bleeder and see if brake fluid spurts out(it will only be a little). If so, and the brakes release(and become easy to turn the wheel and noise disappears or lessens) it is one of three things: collapsed brake hoses, bad master, or improper brake pedal pushrod length.
If the brakes DON'T release, the calipers are most likely in need of rebuild/replacement.
Squeeze the piston back a tiny bit with a screwdriver or a big pair of slip-joint pliers(AKA water pump pliers). I have a huge pair of pliers that will open up about 6" and have 16-18" handles. They are perfect for this job, they can grab the brake pad near the piston and squeeze the caliper piston back in, usually while the caliper is still mounted. You can usually find something to pry on with a LARGE screwdriver too, just don't rip the piston's rubber dust boot.
Replacing brake fluid every two years prevents the corrosion that freezes calipers and such.