my canon pixma tr8620a won't scan using the auto document feeder, it just makes a noise and says error.

Paper is jammed in the ADF path or the paper guides are misaligned.

1. Power off the printer.
2. Open the ADF cover (the top lid where you feed documents).
3. Remove any stuck paper fragments. Pull gently in the direction of paper travel.
4. Check the paper width guides in the ADF tray. They must touch the sides of your document stack.
5. Close the ADF cover firmly until it clicks.
6. Power the printer back on.

If that didn't work, the documents may be too thick, curled, or have staples/paperclips. The ADF is for standard weight paper only. Try scanning a single, flat sheet of plain paper as a test.

Heads up: Always fan a stack of paper before loading to prevent multi-feeds. Ensure documents do not exceed the maximum sheet count for the ADF.