Why do we need this?
I suppose the answer is that if you have never found that you cannot print from a program, you do not need this. However, many users of emulators and DOS programs find that their program will only send output direct to the parallel port, using its own inbuilt command codes. Many modern printers will not even accept plain text sent to the parallel port (that is if they even connect through the parallel port - most are USB nowadays). As printers have developed, they expect Windows to do all of the hard work and convert text and graphics into something which they can understand without having to convert - this cuts down on the cost of hardware, but means a loss of compatibility with older programs.
How do Printfil and QPCPrint work?
Both Printfil and QPCPrint are Windows based programs, set up as pseudo printer drivers on your computer. They look for any output set to a parallel port (eg. LPT1 is the default), then capture this output and convert it into data which can then be printed on any modern printer connected to Windows. This can be done in the background, or you can use options to view the output and decide which printer to use.
Printfil is the only program of the two which can handle a printer which is actually connected to LPT1. However, QPCPrint is more accurate when it comes to printing from a program which expects an EPSON printer.
Try them both and see what you think. We can offer some advice and assistance if you are struggling.