PDF files are everywhere. Every operating system and every device I know of can read them. They are a great way to share and publish files since they can be locked, watermarked, and viewed on pretty much any device or OS. Most office suites allow you to save files as PDF formats and there are some other great tools for creating them.
Sometimes you have multiple PDF files that you want to combine into one. I do this often since I save scanned documents as PDF files, as well as much of my own work.
PDF Mergy is a Chrome web app that makes it easy to merge PDF Files. Drag and drop or select from your computer, place them in the order you want, and then, viola, one merged PDF file. It is all done on their server, not your computer, so this is a great app for use with Chromebooks and for people looking to do everything in the cloud. QuickPDF does the same thing, but needs to be installed on your computer.
Related:
PDF - interesting infographic and lots of resources for using them
Lots of PDF resources - print, markup, convert and more
PDFBinder - simple tool to merge PDF documents into one
BabyPDF - Edit PDF documents for free
Crocodoc - markup PDF files for free
Fill Any PDF form - fill out, sign and send forms
I Love PDF - merge or split PDF files
Adobe Digital School Collection - supporting creativity and digital literacy - includes Adobe Acrobat for creating PDF files
Fill Any PDF form - fill out, sign and send forms
I Love PDF - merge or split PDF files
Adobe Digital School Collection - supporting creativity and digital literacy - includes Adobe Acrobat for creating PDF files