4.1.py

with open("names.txt",'r',encoding = 'utf-8') as names_file:

   # open body.txt for reading
   with open("body.txt",'r',encoding = 'utf-8') as body_file:

       # read entire content of the body
       body = body_file.read()

       # iterate over names
       for name in names_file:
           mail = "Hello "+name+body

           # write the mails to individual files
           with open(name.strip()+".txt",'w',encoding = 'utf-8') as mail_file:
               mail_file.write(mail)