You can create a new subfolder and encrypt it. Each file saved to this subfolder will automatically be encrypted.
How to encrypt a folder:
In the Files oder app's folder tree select the folder in which you want to create an ecrypted subfolder.
Note: Select a folder for which you have the permission to create subfolders.
Enter a name in the New folder window. Click on .
The Encrypt Files window will be displayed. Click on .