Nope, this is not easy, indeed I'm not convinced that it's even possible.
Others should feel free to suggest alternate ways as well.
Your browser does the asking, and the server does the serving. The server cannot "force" stuff to the browser. Thus if the browser asks for the PDF they get the PDF, if they ask for the instructions page, then they get the instructions page.
From what you've described I think I might try somethign like this;
a) create a netwebpage, with nothing but a FrameSet extension. Use the extension to break the page into 2 frames, let's say a top and bottom frame.
b) set the default url for the top to the Instructions page, and the default url of the bottom to the PDF page
c) create a separate Instructionspage procedure (or static htm).
Then when the user clicks on the URL to get the report, make sure it's the Framepage (created in (a)) that the URL points to.
That may well do what you are chasing, and keeps the instructions, and report together.