Hi Jörg,
The current option in Chrome is "Download PDF files instead of automatically opening them in Chrome". By default, this option is disabled.
It's my case and the PDF file is always downloaded from Allplan Connect.
To be sure, I did a short test on my website. A simple "<a href="./my_pdf_file.pdf" >My PDF file</a>" works perfectly (with or without target="_blank".
It seems that to force a download, it happens in the .htaccess file by having indicated for the PDF files "ForceType application/octet-stream Header set Content-disposition attachment".
I don't know how it works in Typo3, but I hope there is a solution. It would be more "comfortable".
In addition, an option to resize large images would be appreciated. Today we have scrolls but that does not allow to have the whole image without having to right click for "Open image in new tab".
Thank you...