Disc pads dragging on rotors

1975 Duster, slant 6, auto, had factory installed disc brakes on front, drum on back. Last trip out on long cruise. After we had been driving for a while, over an hour, we noticed whenever I had to apply heavy pressure to the brakes, we heard a grinding noise. Light pressure on the brakes, we didn't notice the noise. After returning home, I pulled one wheel. The rotor surface is wearing unevenly, looks to have plenty of thickness still but but due to the unevenness of the wearing probably should be turned. I could not pull the caliper off, more to come about this. What I could see of the pads, they seemed like they have thickness still although I could not measure them to be sure. I removed the 2 bolts/brackets that hold the caliper in place but the pads are tight against the rotor surfaces. The pads being tight against the rotor is the reason I couldn't get the caliper off. So my question is, should these pads be this tight or should I be looking for a specific problem? Thanks in advance.