I’ve changed my phone and copied the whole CamScanner folder to the new phone, but when I open CamScanner app on the new phone, the copied documents do not show up. Why? How can I restore those documents?
The CamScanner files CANNOT be restored simply by moving the [CamScanner] folder to the new phone. If you still have access to your old phone, you have three ways to transfer data:
1.With sync feature
If you have a CamScanner account in your old phone, please sign in to CamScanner on www.camscanner.com to check your files there.  Then sign in with the SAME CS account on your new phone, your files will be downloaded automatically. If you don't have a CamScanner account, you can sign up for it either on the web or in the app and then sign in on your old phone to sync files.

2. If you have backed up the data in CamScanner by clicking CamScanner settings - security & backup - backup on your old phone, you can restore your data by moving the [IntSig] folder into the root directory of internal sd card of your new phone and then clicking CamScanner Settings->Security & Backup->Restore.

3. The last way is to import the images into CamScanner maunually.
The images are saved in /CamScanner/.images/.bak (It is a hidden folder). You can select and share them to CamScanner in your phone again. Sorry that all file names, tags and notes cannot be restored in this way.

As CamScanner files cannot be restored simply by moving its folder in sdcard, it is recommended to back up CamScanner data by the CS cloud service in case of any unexpected data loss.