Unfortunately I can't create another email.!
Here's what display the console when I try to preview a pdf:

Yes...the html works.
Now I try to see if there is an error and if I can create a new mail so you can test it.
Thank you in advance!!

If I just left click on the pdf icon this is the result:

Inspecting the page I got this:

Is a domain related email of www.aruba.it , an important italian provider.

I've notice that if I right click on the pdf icon it opens options and if I click on "open" instead of "preview" it will open a new tab and the the viewer works ok.
So the problem is the preview

Yes, I've tried with my yahoo webmail but I think they have a direct viewer so it works.
If you got a link to test I can try

When I try to open it inside the webmail page appears an inside tab who asks me to install a pdf viewer with a link to Adobe Reader.
Always the same thing even if I select to open the pdf in an external viewer from the Opera options

So no other options than using a browser that doesn't suffer this problem.
After such many years using Opera this is a really sad way to end it

Re: Can't open Pdf files in browser

After many months I'm trying to solve this problem before giving up and change browser (Edge or Firefox don't have this problem)
Is there any solution? Someone can help me?