Idee für besser UI

I think you need to consider the ellipses — those three dots after the truncated name of your PDF file open in the tab — before going much further with this inquiry.

What's the full name of the PDF file you have open in that tab?

Do you want to extend the tab for your open PDF window to be long enough to accommodate any name for a given PDF file? If you do, you're likely going to have a lot less room for multiple tabs in Acrobat without truncating the names. 

If it concerns you, I'd suggest filing your complaints with Acrobat UserVoice. This will register your concerns with Adobe developers who have sway over how Acrobat's UI operates. This forum is populated with end users, just like you (and me, for that matter) who may be able to help you with technical issues using Acrobat. We don't have the pull to change the software UI.

Randy