There's no way to really cover all the possible ways in which upgrading from v4 to v7 could happen, so in reality there is only one tip: Test, Test, Test!

It's extremely important to install PlanetPress Suite on a test or development machine, to migrate all your information and test everything very thoroughly before "pulling the plug" on the old server. Test everything you can think of, and even what you can't.

As for creating PDFs, in order to do this you could either upgrade to a PlanetPress Office or PlanetPress Production licence (they didn't exist back in version 4, and Watch won't create PDFs on its own), or you could purchase a PlanetPress Imaging licence, which would also give you the ability to output to different formats, and to output to FAX.

You should probably speak to a sales agent in order to learn the differences between those licences and make sure you get exactly what you need.

A great resource for learning about version 7 would be the OL Learn website. Assuming you have a valid OL Care maintenance contract, you can access it on http://ollearn.objectiflune.com/