DIAGNOSIS Smudging is almost always caused by wet ink getting dragged before it dries. This points to an issue with the paper path or the ink itself not drying fast enough on that specific paper.
FIX First, check your paper type setting. 1) On the print dialog box on your computer, click 'Properties' or 'Preferences'. 2) Look for 'Paper Type' or 'Media' and make sure it matches what's in the tray. If you're using plain paper, set it to 'Plain Paper'. If it's set to 'Photo Paper' or 'Glossy', it lays down too much ink for plain paper, causing smears. Also, ensure you're loading paper printable side up (check for a watermark or feel for the smoother side).
IF THAT DIDN'T WORK There might be a buildup of ink or debris on the paper path rollers. Unplug the printer and inspect the black rubber rollers you can see inside (like the paper output roller). Clean them with a damp, lint-free cloth. Also, check if there's any leaked ink inside the cartridge carriage area that the paper might be brushing against.
HEADS UP Avoid handling freshly printed pages right out of the tray. Let them sit for 30 seconds, especially if you're printing graphics or solid black areas. Using the wrong paper type is the #1 cause of this smudging problem.