For a reason still unclear to me, the PDF engine refuses to embed fonts if the file name is empty (so fonts that are loaded directly from byte arrays typically). It could be that this in itself is outdated. However, embedding fonts that are loaded from the file system has worked so far, but in Qt 6.8 we moved to the DirectWrite engine on Windows and this stopped working there. The reason is that our custom file loader did not support tracking the file name and thus it would always be empty. This is experienced as a regression and can only be worked around by manually selecting the GDI engine instead (with the limitations that implies). We fix this by implementing the loader as a IDWriteLocalFontFileLoader instead, which supports the API which we currently use to retrieve the paths of system-wide fonts. Pick-to: 6.8 6.9 Fixes: QTBUG-134695 Change-Id: I1411b0617fd1c113c7c28154968c234920f5289e Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>