Print head alignment is one of those maintenance jobs nobody does until something looks wrong. Usually it's text that's gone slightly soft around the edges, or a table border that prints with a faint ghost line running alongside it. Vertical lines are the giveaway. If they look doubled, the head has drifted.
A new cartridge will do it. So will moving the printer, or a knock, or nothing identifiable at all. Either way, the fix is the same, and it takes about five minutes, most of which is waiting.
Getting to the tool
The printer needs to be on and connected, USB or Wi-Fi; it doesn't matter which.
If you've never installed Canon's software on this computer, get the driver package for your model from Canon's support site first. The disc in the box is a trap. It's older than whatever's online, and on Windows 11 it frequently refuses to install at all, which sends people off troubleshooting a problem they created by using the CD.
Once it's installed, you're looking for a utility with a name that varies by model. Canon Printer Assistant, usually. Canon IJ Printer Utility on a Mac. Type "Canon" into your Start menu or Applications folder, and whatever's there will surface.
Inside it, find Maintenance. Might be a tab, might be a button, might be labelled Tools or Settings instead, depending on which version you've got. All the cleaning and alignment functions live together in there.
Running it
Look for Print Head Alignment. Some versions offer automatic and manual as separate options.
Take automatic. Manual alignment means printing a sheet of pattern blocks, squinting at them, deciding which one looks least bad, and typing that number in. It's tedious, and it's easy to get wrong. Only bother with it if automatic has already failed you.
Load plain paper. A4 or Letter, whatever your printer normally eats. Not photo paper, not letterhead, not anything with a texture. This matters more than it sounds like it should, because the printer scans this page back in and reads it optically. A glossy surface or a watermark skews what it sees, and you get an alignment based on bad data.
Then press start and let it print. What comes out is a page of grids and line blocks that looks like it means nothing. It doesn't mean anything to you. It means plenty to the scanner.
The bit that goes wrong
Now you put that sheet back on the scanner glass, face down, and this is where most failed alignments happen.
The orientation is specific. The software shows you which way round it wants the page, and people glance at it, assume it's obvious, and put it in the other way. Sometimes you get an error. Sometimes, less helpfully, you get a successful alignment that's actively worse than what you started with.
So look at the diagram properly. Ten seconds.
One more thing: if your printer has a document feeder, don't assume that's where the sheet goes. Plenty of Canon models want the flatbed glass for this specific job even though the feeder sits right there. Check what the software says.
Finishing up
Close the lid, confirm, and wait. The software reads the patterns, calculates the offsets, and writes them into the printer's memory.
When it tells you it's finished, print something you know well. An old document, anything you've printed before and can compare against. Text should be sharp again. Lines should be single and clean, no ghosting.
If they're not, alignment probably wasn't your problem. Run a nozzle check instead, because a partially blocked nozzle produces gappy, faded output that looks a bit like misalignment but won't respond to it. Clean the head, then align afterwards. In that order. There's no sense aligning a head that isn't firing properly to begin with.