'Create Multiple PDF Files' won't open .docx files

Hi,

I am using Acrobat Pro DC (Build: 17.12.20095.239572) on a MacBook Pro (OSX Sierra 10.12.6). I am using the Create PDF - 'Create Multiple PDF Files' menu, and have had success with this process for file types that include .jpeg, .tiff, .txt, .pptx. When I try to use this 'Create Multiple PDF Files' menu for .docx files, the .docx files themselves are greyed out and cannot be selected. However, if I use the Create PDF - 'Single File' menu, .docx files are not greyed out and can be selected (obviously I don't want to repeat this process for hundreds of invididual .docx files). I have a licensed copy of MS Word (version 15.37 - 170815) installed on the MacBook. Any ideas? Let me know if you need further info. Thanks for any help in advance.