Valid from List & Label 21
If you want to generate only PDFs with arbitrary format, you can use the following steps:
a) Do not set Force Paper Size, that only chooses the correct paper format if such a size is available, otherwise it chooses the next best one (smallest that the project fits in completely) and that might cause an unexpected paper try choice or such.
b) Do not set Size Adjustment to "Fit", otherwise the project will be scaled to the whole paper size when printing.
c) Your task is non-trivial as printers often have a larger or smaller unprintable area (frame) around the actual printable area on the paper. This means you either choose "No" in Use Physical Page, then the positioning of the object is relative to the start of the printable area and the position of the label is "floating" with different devices, or you choose "Yes" and must make sure no object can ever appear in an (unknown) printable area as the label is positioned in relation to the top left edge of the paper, not the printable area itself.
d) You can get the available paper sizes of a printer (driver) either by running our DEBWIN3 tool, and calling LlSetDebug(LL_DEBUG_CMBTLL|LL_DEBUG_PRNINFO), or by looking in the list of papers in the printer driver's options dialog (for example Control Panel > Devices and Printers > right-click on a printer > Printer Properties > Advanced > Printing Defaults > Advanced). There are 118 defined paper sizes (like A4 and letter) in Windows, but every device can add its own sizes if it supports any.
Best you can do that far is using XPS or a PDF printer driver on the server, and choose your label format as paper size, so that the LL file does not depend on the paper. Most PDF printer drivers as well as XPS do support a lot of paper sizes, so you should be able to find a suitable solution.
If your printer driver does not support a matching paper format, you can define your own (at least for XPS and PDF) in Control Panel > Devices and Printers > Print server properties > Forms > Change Form Settings > Create a new Form, which is then available in LL's printer settings (after restarting the app that hosts LL as LL caches the paper sizes).
In combination with the above settings (a)-(c) clients are able to print the label on any device they have by choosing their printer in the print settings dialog.