PDF Joiner - This online tool allows you to join several PDF documents into a single file, free of charge.
Documents by Readdle - A central hub for all your files.
PDFChef Merge PDF - PDFChef Merge PDF is an online tool that allows you to merge multiple PDf files into one quickly and securely.
FileApp - FileApp is an iPhone and iPad File System and Document Viewer.
PDFill - Open, View, Edit, Save and Print PDF Documents without Adobe Acrobat
FE File Explorer - The one-stop files solution