There may be times when you need to perform merges, splits, or encryption on a PDF file but don't have access to software on your PC that can perform those tasks. This is where the free Sejda web service comes in.

the process is simple: 

1. Select the task you want to perform
2. Upload the file
3. Define the tasks parameters
4. Voila 

The web interface is clean and the service is super easy to use.

I tested it out with PDFs up to the service maximum and the service worked quickly and flawlessly.

As a security guy, my one caveat would be :

Don't use any web service for hyper confidential information

As of November 2012, the service supports up to 10 file uploads per task totalling up to 50mb in size.

The service also has a rotate feature. It can rotate pages 90, 180 or 270 degress. The rotate function can be performed on all pages, odd pages or even pages. Of course you can also rotate a single page.

Overall this is a nice service to keep in mind. It may just get you out of a bind one of these days.