I have Windows 10 installed in a 1 TB SSD (C:) and I want to use linux. To do so, I want to a backup of C:\users\me to (E:), that is a 1 TB HDD that I want to use as storage.
Is it possible to reformat C:\ changing OS, without altering E:'s content in the process? Can I keep the data safe? Is this a good idea? how hard could it be?
Is this a good idea? .......... No. Lots of stuff in Appdata that does not move easily. (Most of your software installation setups). User Profiles can be backed up but not readily moved. In the worst case, you can break your OS.
Back up your data, then format and set up things properly.
You can move and back up My Documents just fine if that satisfies you.
Another solution is to set up Linux in a Virtual Machine. I do this (VMware and Hyper-V both) and this is a solution that works very well and if safe for your host OS.
The VM solution lets you test the Linux you selected and then determine if something else fits your needs better.
I also note that you are using Windows 10 which goes out of support in a few months. VM's can be backed up and ported simply to a new machine.