It is probably not a LPT to serial adapter. Serial port has 2 types of pinouts, of which the 25 pinout is practically the same as parallel port pinout, so you have probably only serial-serial connector instead of parallel to serial adapter. See also this answer.
The parallel printer can be connected to PC with USB cable that is called something like USB to Centronics Printer Cable
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For using the printer form DOS (under Windows) as LPT1 see this answer.