How To Move A Page To Another Documentation?

Scenario

You have a page P in some documentation D. Now you want to move P to another documentation E.

Solution

As each documentation has it's individual space version history, there is no option available to move a page across different documentations.

Thus, the basic idea is to create a new page Q in documentation E, copy the content of page P to page Q, and remove P afterwards.

Step By Step

1. Go to page P in documentation D.
2. Edit page P.
3. Copy all content from the editor by using CTRL+A, CTRL+C / CMD+A, CMD+C. 
4. Close the editor again.
5. Open that page in documentation E under which you want to "move" page P.
6. Create a new page Q.
7. Paste the content you have copied in the editor.
8. Publish page Q.
9. Open page P in documentation D again.
10. Delete page P, and make sure you select option Remove page and all its versions