PDFpen 4.5.3 gained a new script for merging documents. It’s called “Merge Every Other”, and is accessible from the Script menu in PDFpen’s menubar. It’s useful for merging two documents when you want the pages from each to interleave.
You need this if you scan one side of a document with a sheetfed scanner, and then turn it over and scan the other side to a separate file. The result is two files: one file of all the odd pages, and another of all the even ones. This script enables you to bring both together in a single ordered document.
To merge the documents, first open the document with the odd pages, and then choose “Merge Every Other”. It will prompt you for a file, select the file with the even pages, and leave the rest to PDFpen!