PDFs generated through Qfield atlas print are not synchronized

[meyerlor]

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PDFs which were created via atlas print are not uploaded into the cloud. QGIS is configured that the PDFs are saved into a subfolder of the project /Kontrollberichte :

This works, I can see the files within Qfield when opening the project folder:

The subfolder itself is configured via Qfield Sync to be synced (this is working well for pictures, they are getting uploaded)

Am I missing a step? How can i bring Qfield to upload those pdf's into the cloud?