What is the best way to send customized letters?

I am trying to figure out how I can send the same general letter out to all my clients with a few personalized details without having to create a separate form for each client. Each client will get specified codes for their family as well as general information that will go to everyone. I want to ensure that all specific information given remains confidential but am unsure how to do so if I only have the one form that I customize that maintains the same URL link. I have attached the letter below that I am attempting to convert into a Jotform. I will be adding a signature at the end to confirm receipt of the letter. Please let me know the best way to do this without having to create a separate form for each new client. Thank you.

I would just like to confirm if you are looking to share the username and password (which are different) for each person, while all the rest of the info is the same?

If so please note that adding username and password to the form would not be good as it might result in your forms being suspended, but you could add such things into the email.

However, even if in the email, it would be good if you can tell us if the username and password are pre-built or if you will make the both based on some selection on your jotform?

Do give us as much details in regards to what you are after as possible and we would be happy to assist with them.