Foxit PDF Editor allows you to merge two PDFs by interleaving pages, a useful feature especially when you need to combine two PDFs (scanned from a double-sided printed document), one PDF with all odd pages and the other with all even pages.
Extraction is the process of reusing selected pages of one PDF in a different PDF. Extracted pages contain not only the content but also all form fields, comments, and links associated with the original page content.