The best method of "locking" the PDF would be to flatten it, which removes all interactive form fields and replaces them with thier appearances. To make the file as uneditiable as possible, it should then be protected with a digital certificate.
You haven't stated it explicitly, but the process you've described does not seem to be performed inside Acrobat, but rather on this "external e-learning platform", which makes it sound like a server based process. Therefore, operations on the PDF are limited to the capabilities of that platform. Unless Acrobat is somehow involved in this process, this is not a question that can be answered here. You need to direct this question to support for the e-learning platform.