How to change document how to change page size in pdf document in Illustrator CS6 and earlier. This process was changed in Illustrator CS4 with the introduction of multiple artboards. If you need to know how to change document size in Illustrator, you first need to check what version of Adobe Illustrator you’re using.
However, in Illustrator CS4, the concept of Multiple Artboards was introduced, meaning that just a single document settings dialogue box was no longer enough to cope. This opens a dialogue box that enables you to enter the values for a single page size. Illustrator CS3 and its previous incarnations also allowed document size to be changed simply by providing a dialogue box into which the user entered the new values, just like so many other layout programs. A dialogue box will appear that enables you to either select a preset standard page size, or enter your own values.