My 64GB iPad 2 is being filled up with loads of pdf service manuals that I use when repairing electronics gear. The crazy thing is that most .PDF files are secured meaning I can't join them together using a program called Preview on my Mac. It means I have around 50 individual .PDF 'booklets' for the one piece of gear. Has anyone a way of joining PDF files so they would show on the iPad in iBooks under one thumbnail? It would be great if Apple could include this feature to iTunes so that it became a simple drag and drop to place a group of PDFs under one Heading and therefore cleanup a busy and confusing looking iPad 2 iBook shelf. Any thoughts anyone?