editable PDF_is it possible?

A file can always be overwritten, unless you have full control over the permissions of the file and the folder where it's located.

Editing a file is a different matter. The best way to prevent it is to digitally sign it. While that doesn't stop someone willing enough to edit it, if they do so it will immediately invalidate the signature so you could prove the file has been edited.

You can also apply to it a file-open password. That will also make editing it much more difficult, as it encrypts the contents of the entire file.

No, forget the idea. While Acrobat does allow you to set "do not edit" security, it is widely ignored by other apps. Your students WILL be able to edit these files. Even if you stopped it, if the info is worth having, it can be copied or retyped. You must expect this to happen and plan accordingly.