PDF Joiner - This online tool allows you to join several PDF documents into a single file, free of charge.
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
DocuPUB - DocuPUB is an online file converter, file merger, file compressor, and file resizing tool.
Dr.Explain - Dr.Explain software is a help file authoring tool.
PDFChef Merge PDF - PDFChef Merge PDF is an online tool that allows you to merge multiple PDf files into one quickly and securely.
CHM Editor - Best solution to edit CHM files