Output files do not have fonts or font sizes. A file is just a collection of bits.
Devices that print or display data have fonts and font sizes (and many other interesting attributes).
Controlling the font that a user sees is a function of the device that the data is being viewed on.
In many (but not all) cases the file format can be used to provide helpful information about fonts and other display characteristics to the device. Often this information is mediated by an intervening bit of software -- such as a web browser, a PDF viewer, a print driver or a terminal emulator.
The specifics depend entirely on the type of file being created and the device that it is being displayed upon.
Progress does some rudimentary support for screen devices via protermcap on UNIX and GUI specific widgets for Windows.
The only nods that Progress makes to printers are newlines and form-feeds.
Beyond that you need to research the target device, whatever software you plan to use to deliver the data to that device, and the specific format needed to get the results that you are looking for. Progress will then allow you to create an appropriate output file -- but there is no magical one size fits all pre-built solution.