Your initial post mentioned one specific app a the default with an image of the result shwoing a "PDF" icon and not Chrome - hinting that the app was the culprit. When I see something like this... it's usually the Freeware app that is the cause as Freeware is always "free" with limitations that help get users to purchase an enhanced version of the app. Many freeware photo and video editing apps place a logo or website address in the end product images/videos that go away if you pay for the non-freeware version. Many people don't like that the freeware app places that logo, but it part of the distribution/usage agreement for using those products - hence why we don't allow discussions of how to disable.
With your clarification - I'll admit that I have NEVER seen this issue and certainly not when a browser like Chrome is the default. If it were my device, I'd uninstall any 3rd party PDF viewer, restart, and check again before chasing other settings. If you want to get some input from designers/coders - you could also check with the
XDA forums.