Hello. A .prn file is a raw printer output file. Windows creates it when a print job is sent to a printer driver that is not completing the job, so instead of converting the document to PDF, it just dumps the print data to disk.
Try this:
- Go to Settings > Bluetooth & devices > Printers & scanners.
- Click on Microsoft Print to PDF.
- Select Printer properties (not just "Properties").
- Look at the Ports tab.
- Ensure the port is set to PORTPROMPT: (Local Port). If a box labeled "Print to file" is checked anywhere in the print dialog when you are actually printing, uncheck it.