When telling Acrobat to combine DOC/DOCX or XLS/XLSX files Acrobat must use its PDFMaker.
Acrobat asks the OS to open the file(s) native application (Word or Excel for your situation) and then has PDFMaker output a PDF.
Acrobat then combines these PDF files.
But, Acrobat 9 PDFMaker is not compatible in Windows 7.
You can use the Adobe PDF printer to output a PDF from the Word / Excel files then, as you noted, combine the PDFs.
Acrobat X provided a Windows 7 compatible PDFMaker.
However, Acrobat X has been replaced by Acrobat XI.
So, to do what you desire you'd need to upgrade to Acrobat XI.
The available upgrade paths are here:
Acrobat 9 is supported on Windows 7.
Can you please let me know couple of things:
1) Bittage of OS i.e 32bit or 64bit
2) Office version
As you re-installed, i hope that you updated to latest path i.e 9.5.2. Am i right?
I can confirm that AApro has now let me update to 9.5.2 (where at once it would not let me) and i can now merge documents
Thank you for your help