Add Document Margins to Illustrator Artboards

It’s astonishing that something as simple as margins still hasn’t been implemented in Illustrator. I often use it for designing flyers, banners, and other print pieces if I need to work with vectors that I want to be able to edit in the same app. 

Having to create a rectangle the size of your document, manually resize it, center it, and then convert it to guides is such a roundabout way of doing something that InDesign does natively.