How do I lock a document so that when a client sends me her responses in the fillable form, I am not able to edit her responses? Can I lock/save it permanently?
Yes you can. You can associate a JavaScript with a form field which will lock the field (make it Read-only) under conditions that you specify. You can also create a document-level JavaScript which locks all filled fields when PDF is saved. This way the user can edit info in a field until PDF is saved. After that the field is read-only.