Link to documents from several nodes What would be the best way to set up several nodes so that some of the content is linked to a single document stored on the server? 
For example, I want a document that has some official rules on it and display it on several pages by only editing the source document.
If you want to display a common piece of content on all the pages, you can  create a block with the common content, and display that block in the content region of the required pages.

Just go to /admin/structure/block and position the block before or after the Main page content block, and set it to only display on the required pages.