Changing title of open file using Acrobat Pro

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I used Acrobat Pro for two years in my previous job, and I had learned a trick to be able to change the name of the file while it was open and I was working on it.  I do not remeber how to do this, and I cannot figure it out or find the answer on the internet.  This was a very useful trick. 

(I remember that I would access this feature by typing something into the "Search tools" box on the right-side of the screen.)

*The answer is NOT:  File  >  Properties  >  Description.  When I do this, I am able to edit the document Title, Author, Subject, and Keywords, but I an not able to edit the document Name.  

Thank you!

[Bernd Alheit]

Use File > Save As and save the document with a new name.