how not to change returned values?

[xmlmagician]

Hello all

I hope you are well. I am using adobe designer 7 for the creation of a survey (nothing new or exiting there :-)). When i complete it and email it as a PDF (by button not the submit email function) the copy i receive can be changed which is not good if you have a satisfaction survey for a department and when they receive it they can change things. I have been looking high and low but i have not had any success so far. thank you in advance for all your help