@Ralf_Stockmann and @Alon1 have you tried…
Also, on my Discourse I use this method…
Embed a PDF from Google Drive
(This is my preferred method so PDFs in iFrames are responsive - other methods mostly fail at being cross-browser responsive.)
- Share
- Copy Share Link
- Open Share Link in a New Tab
- Click the 3 Vertical Dots in the Top Right Corner
- Select Embed Item
- Copy the Displayed iFrame Code
- Paste it in the Discourse Editor
A Test PDF on Google Drive is embedded here below which you can << Download Here >>
<iframe src="https://drive.google.com/file/d/1KQ-jn7R0NmZxw955QaPu3lvLFh5zpnDe/preview" width="640" height="480" allow="autoplay"></iframe>
This is what it looks like… (which you can also try out live HERE on my site)