MyPIXMA TRS 8520 had been printing ok. When it gave the "out of paper" message, I reloaded in my usual way. First the message was "no paper in rear tray." The only tray I have loads from the front. I checked the paper guides and made sure the paper was secure. I then tried again. Some of the times it said there was a jam. The "jam" turned out be one whole piece of paper was under the paper tray. I took the tray out and made sure the tray was as high as it could be and still go in. Then I had a choice of selecting print, scan, etc. Under print, the choices were template, cloud, and memory card. My closest of the three would be template, whose choices were various types of lined or graph papwe, but no standard blank, letter-sized paper.
The PIXMA TR8520 has two paper sources, the front cassette and the rear tray. When printing, some applications default to the rear tray.
You can change the setting in the application that you are printing from or load paper in the rear tray, and print from that location.
To load paper in the rear tray, please follow the steps from the manual: