I have purchased a recycled HP laserjet 2420n with no CD. I did the plug and play and my PC recognises that it is there but then asks me for the HPPaufd0.sys file. I have searched for it. I have gone into c:/windows/system32/drivers etc and cannot find it. I have looked it up on the internet and been informed that Hppaufd0.sys can sometimes contain viruses and it may have been removed. I really just want to be able to print!!

Hello,
You will need to download the correct driver for your OS from this HP website. http://h20000.www2.hp.com/bizsupport/TechSupport/DriverDownload.jsp?lang=en&cc=us&prodNameId=412129&taskId=135&prodTypeId=18972&prodSeriesId=416419&lang=en&cc=us
Install the driver and plug the printer back in. It will now find the new driver and will have all the support files as well.
If you continue to have issues, temporarily disable your viruses scanner while you install the driver. The drivers from HP's website contain no viruses so your scanner may give a false positive if it tries to remove any files while installing.
Regards, Chris