I've tried tried disabling it in the startup apps, closing the tray icon and terminating it in the task manager yet it keeps on popping up in the task manager.
How can stop it from running in the background?
The autostart is controlled by the Windows registry. The installer adds an entry here:
SOFTWARE\Microsoft\Windows\CurrentVersion\Run
Look for the PDF24 entry.
Why is this entry needed?
This autostart entry creates a pdf24.exe instance for the user. This instance is required for the PDF printer in order to receive and process print jobs from the PDF printer.
There is also a Window service installed that also uses a pdf24.exe instance. This PDF24 Windows service is also required for the PDF printer. The service receives a print job from the PDF printer and identifies the user who printed it. The print data is then transferred to the user's corresponding pdf24.exe instance. There, the print data is processed, and usually the PDF24 Assistant opens, allowing the user to, for example, save the PDF.
So, if you want to stop the pdf24.exe user process, delete the following Windows Registry value:
SOFTWARE\Microsoft\Windows\CurrentVersion\Run\PDF24
If you want to stop the pdf24.exe Windows service process, stop the corresponding Windows service named PDF24. If you stop the service, then the PDF printer will no longer work. Print jobs are then stuck in the print spooler. You then have to start the service manually to make the PDF printer work again.