In order to save a form so that it cannot be edited but is still fillable, you will need to take the following steps:
1. Open the form in Adobe Acrobat
2. Go to 'File' > 'Save As' > 'Reader Extended PDF' > 'Enable More Tools (includes Form Fill-in & Save)'. This will open up additional options in the sidebar
3. In the sidebar, go to 'Protect' > 'More Options'
4. In the next menu, select 'Document Printing', 'Fill in Forms', and 'Content Copying for Accessibility'. Then click on 'OK'.
5. Enter a password if you want and click on 'Save'.