In recent versions of the Chrome app for Android (begin of 2025), you may find that tapping link pointing to a PDF document, will open the internal PDF viewer instead of your preferred app (mine is MuPDF viewer). On the net you may find several recipes to disable that behaviour, but they are eventually outdated (they refer to the Settings ⇒ Privacy and security ⇒ Site Settings ⇒ PDF documents, which does not exist anymore).

Also the the advice to go to Settings ⇒ Apps ⇒ your PDF viewer ⇒ Set as default is useless.

The solution of the problem now requires to open in Chrome the special link:

chrome://flags/

Then search for the Open PDF Inline on Android and Open PDF Inline on Android pre-V options and disable them both.