Hi there-to do this, open the app which holds your PDF. When open, there will be a square with an arrow sticking out in the upper right hand corner. Press that and it will attach to your email by opening up your email page to compose your letter.
Also, I have deleted your other post as it was a duplicate of this one. Please do not do this as it is against forum rules and makes it hard for others to follow and participate when there are multiple threads present.