If you want to edit a read-only PowerPoint file , you have to unlock it. This article will show you how to lock and unlock PowerPoint files for editing with a few simple steps.
Unlock read-only PowerPoint files
There are two ways to tell if a PowerPoint file is read-only. The first is to see the phrase “Read-only” after the file name, and the second is to see a yellow notification bar at the top when you open the file with a message saying that the document is restricted.
Next to the yellow message is a button that says Edit Anyway . Click that button to unlock the PowerPoint file.

The yellow bar will disappear and the words Read-only will appear after the file name. The PowerPoint file is now editable.

Another way to unlock a PowerPoint file is to go to the File tab .

You will be taken to the Info menu. Here the Protect Presentation option is highlighted in yellow and has a message “The presentation has been marked as final to discourage any editing” displayed next to it. Select Protect Presentation .

From the submenu, select Mark as Final to unlock the PowerPoint file.

Now, you will see that the yellow banner and notification next to the Protect Presentation option is gone. The Read-only phrase next to the file name is also gone.

How to lock PowerPoint files read-only
Now that you know how to unlock a PowerPoint file and why you might need to lock it, here's how to enable read-only mode.
Open the PowerPoint file you want to leave unedited, select the File tab .

You will be taken to the Info menu. Select Protect Presentation to open the drop-down menu, click Mark as Final .

A dialog box appears notifying you that the PowerPoint file is marked as final and saved, click Ok .

Now, when sending a document, it will display the Marked as Final bar, informing the recipient that this PowerPoint file is read-only and cannot be edited.
Why do I need to set PowerPoint files to Read-only mode?
People use this mode to restrict editing, simply notifying the recipient of the PowerPoint file that it is the author's final version. Read-only status can also prevent accidental editing of the document.
Leaving a document in read-only mode is a more polite way to ask people not to edit it and protect your content. Taking steps to let people know you don't want the content edited is the right thing to do.
If you want to set a password to completely block viewing and editing PowerPoint files, you can refer to this article on how to set a password for PowerPoint .
Good luck!