Hello,
the easiest way to get a PDF in the page size of your Word document is to convert the Word file instead of printing it: drag the file into PDF24 Creator or use "Convert to PDF" in the PDF24 Toolbox. PDF24 then lets Word export the PDF itself, and the pages keep the size set in the document, for example 80 x 120 mm.
This also works online: https://tools.pdf24.org/en/word-to-pdf
If you want to print: the classic PDF24 printer supports custom paper sizes, including forms created in the print server properties of Windows. The driverless PDF24 printer (Windows 11 24H2 and later) only offers a fixed list of standard sizes; you can add a classic printer in the PDF24 settings. Details: https://creator.pdf24.org/manual/11/#63-classic-and-driverless-pdf-printers