Additional files need to be installed to create PDF from this file (Excel). You must have Administrator Privileges to install these files

Not the correct answer - sorry! Makes absolutely no difference. My PC, I already am the Administrator and already run Adobe Pro DC as Administrator - went through all this with Adobe - here is the transcript:

Laboney: Hello! Welcome to Adobe support.
Barclay Lamont: Hi, When I try to combine files it does not recognise Excel. If I paste the file it says I need additional files and to contach the Administrator - I am the Administrator. Office 356 Windows 10 pro. Can you help please?
Laboney: Please allow me 1-2 minute(s) to review your account details.
Laboney: May I have the serial key for the software ?
Barclay Lamont: xxxxxxx
Laboney: May I know the steps that you are following to combine the files ?
Barclay Lamont: Select files, right click, combine files in Acrobat. Been doing this all day until I installed Office 365
Laboney: Is it happening with all the files or with the a particular file ?
Laboney: Please try to follow this steps :
Barclay Lamont: Word is fine - the problem is with Excel
Laboney: Launch Acrobat >go to tools >combine files
Barclay Lamont: Yes - have done all this, am there now and it says "Additional files need to be installed to create PDF from this file (Excel). You must have Administrator Privileges to install these files"
Laboney: Okay please cancel Acrobat then Right click on Acrobat icon and choose Run as administrator
Barclay Lamont: It asks me if I want to run repair mode - I have already done this
Laboney: Try it
Barclay Lamont: Done - asks me if I want to run in repair mode - I ran repair mode and got the SAME MESSAGE.
Laboney: Okay
Laboney: Could you please attach the screen shot of the error message page ?
Barclay Lamont: How?
Laboney: Can you please check if you can print to Adobe pdf in Excel ?
Barclay Lamont: Yes I can. I've been on the net all day looking for a fix - I paid over £400 for this software and it doesn't work!
Laboney: Is it happening with all the excel file or only one
Barclay Lamont: All
Laboney: Try to convert the excel with acrobat plug in
Barclay Lamont: I told you I have tried this. It converts XLS files of but the newer versions it does not recognise XLSX in a combine batch
Laboney: Okay please follow the below steps :
Laboney: May I know when you open Acrobat what does it says on the top of the application ?Does it says Acrobat pro DC or Acrobat Reader DC ?
Barclay Lamont: Pro DC
Laboney: Okay please follow the below trouble shooting steps :
Laboney: Go to Local C: Drive
Laboney: Then Program Files (x86)
Laboney: Then Adobe
Laboney: Then Acrobat DC
Laboney: Then Setup Files
Laboney: Then {AC76BA86-1033-FFFF-7760-0C0F074E4100} - 
Laboney: Then Acro pro msi
Laboney: Then You wil get the new window
Laboney: Then next 
Laboney: Choose modify
Laboney: Click on next
Laboney: Choose Create adobe pdf plug in
Laboney: Choose the option this feature will not be available and the  install it
Laboney:
Barclay Lamont: working on it
Laboney: Okay
Barclay Lamont: No difference - plug ins not listed - installed Create Adobe PDF
Barclay Lamont: Same error message - Additional files need to be installed - this is VERY frustrating..
Laboney: May I have your call back number please ?
Barclay Lamont: xxxxxxxxxx (UK)
Laboney: I am escalating the case to next level
Laboney: They will get back to you with in next 48-72 working hours
Laboney: This is your case number 0187691632
Laboney: Is there anything else I can help you with?
Barclay Lamont: Oh boy - this is vital for my business. Thought an Upgrade from X to XI and then DC would help - clearly didnt. Thanks for your help but sadly no further forward.
info: Your chat transcript will be sent to b@rclay.org at the end of your chat.
Laboney: I apologize for the inconvenience.
Laboney: Thank you for contacting Adobe.  We are available 7 days a week, 24 hours a day. Goodbye!