Allow a user to upload a PDF file to a specific block within a page
You could use the Entity Reference module to add the "Select a page for the PDF to populate" field (in the "Brochure" content type).

Then, create a View block that filters on "content type = brochure" and which pulls the PDF file field only. Set up a Contextual Filter for the entity reference field (the one that you selected the node/page for the PDF to populate on) and provide a default value of the nid of the page being viewed. 

Placing this block in a region should pull related PDFs for pages that have been referenced. Should work!