Printing to file is a system where a virtual device driver behaves like a printer, but instead writes the data to a file.

What actually happens depends on the context, but generally speaking, file printers produce post-script documents or images that are what you would expect to be printed to paper. Because file printers speak "printer language", any program can use them, and their product can be anything the file printer likes.

PDF Writers are an example of a file printer; a program like word treats the PDF writer like a printer and instructs it on how to "draw" the document. The PDF writer simply collects the data and instead, creates a .pdf file.