PDFTK Builder - PDFTK Builder is a free graphical interface to for PDFTK, making it much easier to use.
PDF Joiner - This online tool allows you to join several PDF documents into a single file, free of charge.
QPDF - QPDF is a command-line program that does structural, content-preserving transformations on PDF...
iSafePDF - iSafePDF is a free open source PDF protection software.
PDFChef Merge PDF - PDFChef Merge PDF is an online tool that allows you to merge multiple PDf files into one quickly and securely.
PyPDF2 - PyPDF2 - A utility to read and write pdfs with Python