How to add text to a PDF document permanently?

I want to add text to a one page pdf document in AA 10.  It is actually a photograph and I want to add a few words of text identifying what's shown in the picture.  I know I can use Typewriter to add this or I can insert a header or footer with the text.  But I want this to be permanent.  When I send the document with the text to somebody else he or she can easily remove or edit my text.  How can I add text to my pdf so that nobody can alter it later?  (I am using AA-10 with Windows 7)