You have already determined that true collation in an acrobat package is not possible, and have suggested using the combine function.
The combine function certainly eliminates the need for collation, but printing double sided creates a problem since the start of one file can end up on the back side of another, without any kind of separation. Is there any way to make it so that the beginning of each file in the binder will start on the front of a page? Other than printing one sided of course.
Create a blank page and export to PDF from your authroing program. Open the Pages panel and scroll the thumbnails to locate the area where a page is to be inserted. Drag the blank page from your desktop to the Pages panel where you want to insert the page,
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The author of numerous books on Acrobat, Photoshop, Illustrator and the Adobe Creative Suite, and an international speaker on Adobe Acrobat, Ted Padova is a well-known PDF guru.