The door rubs the frame or the threshold. When a pivot wears, the door drops slightly at the latch side, and the first thing you notice is a scraping sound or a mark on the frame.
The gap around the door is uneven. Look at the reveal along the top and the latch edge. If it is wide at one corner and tight at another, the door is no longer hanging square.
You hear squeaking or grinding at the top or bottom of the door, or you see metal shavings or rust around the pivot. Bearings that have run dry wear quickly.
The latch needs a push or a pull to catch. A dropped door shifts the latch away from the strike, so staff start pushing it closed by hand.
Finally, the closer seems to struggle. A dragging door puts extra load on the closer, which can make a healthy closer look weak. Replacing the pivots and realigning the door often fixes both problems.