You can concat multiple PDf files together using Ghostscript. This will “print” each of the PDF's to a sudo printer which writes them out as a file. Because of this, the resulting PDF may be larger and could loose some text and features from the original. Works well on scanned PDF's, Faxes, and other similar documents.
gs -q -sPAPERSIZE=letter -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=newsletter.pdf newsletter_page1.pdf newsletter_page2.pdf