Why won't PDFs print correctly?

For some time now I have been unable to print PDF files to my Canon printer.

The printer will print photos without issue, but will not print from a PDF. Particularly if the PDF is a form or shipping label. If it does not print a blank page, then what does come out looks like this:

The printer in question is a Canon Pixma MG6320 connected over wifi.

I have tried:

• Using the "Print as image"option from Adobe Acrobat.
• Cleaning the cartridges
• Replacing the cartridges
• Deleting and re-adding the printer
• Resetting printer data from system preferences
• Printing from Acrobat Pro, Preview, Photoshop. Same result.

Have yet to try manually flushing the print heads out (would prefer to avoid this).

Any ideas? I've wasted a lot of paper on this...