[GeoffR]

A pin reset just forces the device to restart, it is just used to get the device going again if it freezes and the power off/on slider doesn't work. It doesn't delete anything, but if the device is in the middle of writing a file when reset it might result in a corrupt file, so best to avoid it unless there is no other option.

Logging out deletes the database, and synced content. Just like a factory reset, except that the firmware isn't reloaded or updated and sideloaded content is not deleted.

A factory reset reloads the factory firmware from a recovery partition and reformats the user partition, so all synced and sideloaded content is deleted.

Edit: Both logging out and factory reset will delete all settings including your Adobe authorization.

After signing out or doing a factory reset, you need to setup the device again. This can be done either via WiFi, or by connecting to the Kobo desktop. I would avoid using the Kobo desktop if at all possible, WiFi setup seems to be more reliable (assuming your WiFi connection is good and battery well charged).