Decryption failed after sharing with password

  1. I created a PDF File in a folder already shared with another ecloud user synced to both desktops with the sync client
  2. I created an external link with password protection (read-only)

Expected Behaviour: Both user can access the file via web interface and locally after syncing w/ the nextcloud client. The external user can see and download the readible file after typing in the password.

Actual Behaviour: None of the 3 can read the file.
When opened in the browser it says

Invalid or corrupted PDF file


PDF.js v2.5.207 (build: 0974d6052)
Message: Invalid PDF structure.

When I open a (pdf)file locally it seems to be encrypted, as it contains


followed by underscores or not recognised characters.

Any thought on this one?