使用awk将字符串添加到字符串末尾的标题行

I am trying to add a "page number" with the format ### to the end of each header line in my file. The Header lines are always the same constant, but appear at random intervals throughout the document. I have attempted this using SED and AWK, but am open to all suggestions. I tried the following sudo code tailored for my issueI am trying to add a "page number" with the for