When using Adobe Create PDF to combine two .docx files and convert into one pdf file, why does Adobe change the file name that I have assigned to a random assortment of numbers and letters?

When using Adobe Create PDF to combine two .docx files and convert into one .pdf file (frontside and backside), why does Adobe change the assigned file name to a different file name that includes random numbers and letters?  Note: The file name was previously "inserted" into the body of the .docx.

What am I doing wrong or what do I need to do different to avoid?

It hasn’t happened for a long time but just happened again this morning. 

I use a PC MS Pro, and have tried Chrome and IE.  But same results. 

Thx, M