A desktop publishing application from Microsoft that focuses on page layout and graphic design.
There is no automagic way of combining Publisher files, unfortunately.
If this is a one time deal and all you need is a one time print file, then I would create a PDF of the combined pages and print it. I use primopdfwhich is a freebie that has been available since before Office 2007 which MSFT added PDF tools for the first time. Unlike any of the MSFT PDF tools it allows you to append a PDF, and that is how you build your print file.
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https://filehippo.com/download_primopdf/
When you install Primo read carefully and opt out of the additional toolbars and junkware that is often bundled with this type of free software. I prefer primPDF to any of the MSFT tools as it will work with any program from which you can print in addition to the appending functionality.
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For example if you want to add 2 pages from one Publication to another Publication of 10 pages you would first send/print the 10 pages to PrimoPDF, create the PDF file and save it. Then open your second Publisher file and send just the 2 pages you want to PrimoPDF and this time save it as the same file name as the original. You will be asked if you want to overwrite or append the original file. Append and your new PDF will be the combined 10 original pages followed by the 2. Then print the PDF.
If you need a combined Publisher file that can be edited then open both files and copy and paste between them.
I create the two blank pages in the 10 page file, save as a different file name, then go to and click the first page of the other file. I use the short cuts of Ctrl+A to select everything on the page, Then Ctrl+Shift+G to group everything. Then Ctrl+C to copy the entire page of grouped elements. Then switch to the blank page in the other publication and Ctrl+V to paste. I drag or nudge the content and align correctly on the page and then Ctrl+Shift+G to ungroup all the elements. You can use the commands on the ribbon menu if you find them more convenient. Once you get the work flow down you can copy and paste entire pages in a matter of seconds.
DavidF