I have the following Edit Mask AAALAAALNNANNLANNNLA and this is the literal mask ___ ___ _____ ____ _ however once exported to PDF I can whatever inside this field and there is no error nort letters turning into capital etc…
PDF is not ODF, and PDF readers are not LibreOffice. Do not expect that anything that LibreOffice can do, would necessarily be possible with an external format like PDF. (This is a general thought; I haven’t investigated if there something in PDF specification, that allows to implement this without embedding executable scripts into PDFs.)