I downloaded mail-merge-contacts application but i can't edit this in my control panel. Why ?

I need application like this (  https://creator.zoho.com/public/showAppInfo?ownername=fmriorum&callbackUrl=mail-merge )

to realize that idea:

User fills out the form and then  script produce specific letter with  specific blank from form like  this and this file we can download in .pdf or .doc.

Thanks !