'Combine File' tool. Unable to drag and drop 'documents' from Outlook

Hello, 

In Adobe Acrobat desktop version I am unable to 'drag and drop' documents using the 'Combine File' tool for any document attachments in Outlook. I am however able to drag and drop the email itself which has the text of the email, but the attachments no matter the format (e.g. PDF, Excel, Word, Powerpoint) will not attach. 

It doesn't look to be any error so when you're dragging across the item, the expected icon appears to indicate there is no error, however when you drop the item nothing ever appears. I am wondering if this is some sort of preference setting or security setting that is preventing the document being attached. 

I can open the documents absolutely fine and combine 'all open documents' absolutely fine (if it's a PDF) however this drag and drop functionality is quite important for how we use this tool, especially for other document types to a PDF. It's not an option for us to save and upload in combine file due to the volume we process. 

Thanks, 

Dom