permissions: How to restrict access to documents in a folder so that they can only be edited and viewed by the user that loads the file?

I have a file structure with a main folder, two subfolders and several PPT documents in each subfolder. Documents should be able to move between the two subfolders, but the hard part is restricting access to who can see and edit these documents.

I need to set the permissions for these folders so that only the user that loads the document can view / download / edit the document that has loaded, but can not do the same with the other documents in the folder. It is not a problem for users to be able to see that there are other files in these subfolders, I just can not make them download and see the other files in the folder.

Is there a way to configure these permissions in SharePoint? Or maybe to create a list in which users can upload a PPT file (if possible) to limit access to each of the documents?

My manual solution to this problem is to go document by document and grant editing access only to the document that the user loads and not grant access to that same user to the other documents in the folder. The problem with this approach is

  1. It is incredibly manual and with the volume of existing files.
    and this is unsustainable
  2. I think the permissions would be restored if the file is moved
    from one subfolder to the other, in which case I (as administrator)
    I would have to go back and re-grant permissions every time a file
    It was moved.

Any ideas on what I can do to address this problem would be greatly appreciated! Thanks in advance!