all you need to do is to set a password. after this no one can edit/ modify your document.. steps are as follow....
1. Go to Tools > Options. Click on the Security tab.
2. To prevent unauthorized modification, type in a password under “Password to modify,” then select OK.
3. Enter a password. Re-enter your password to confirm. Select OK.
4. Go to File > Save and close PowerPoint.
5. The " Password to modify” will allow anyone to open a “read-only” copy of your presentation. This means no one can make any changes to your documentation unless they know the password.
6. Note: You can go the extra step and require that people enter a password to OPEN the document. Simply enter a password under the “Password to confirm” dialog box. If you set password in this box no one can even see the document without password.
7. The next time you open the document, the dialog box will say “Enter password to modify, or open read-only.” You should instruct the students or colleagues who have access to your document to select “Open read only” when they open your document to prevent confusion.
8. To remove password protection, simply go back to Tools > Options and the Security Tab and remove the passwords