Save as .pdf

Hi, I communicate a lot through email (that’s why I purchased the email-module). It works fantastic, but there is one thing:

On a regular basis I have to write letters to insurance, doctors etc. on my clients behalf. Now I’d like to send these letters as .pdf, since no alterations can be made once it’s created. I use the ‘letter to patient’, or the ‘letter to patient gp’ – report to start with. When I finish the letter I have to save it as for instance .rtf, .doc, .txt, file. When I send this to my client, he or she can modify this to whatever he wants.

What are your ideas on this matter?