This feature is a great tool for extending the size of your document. It lets you position the original design content in the centre, at the top, at the bottom, or on the left or right side of the new canvas and is great if you need to apply borders to your design.
You can access this feature from the Edit Menu > Extend Design Document.
• Extend Canvas By - this option lets you grow your canvas by automatically adding blank borders around it at a specified size.
• Total Size - use this option to specify the overall size of your canvas. When you use this option, the software automatically works out how large the borders need to be in order to satisfy the new document dimensions.
• Apply to - choose to apply the new dimensions to the first repeat of your file, or the current repeat. The current repeat is the number of repeats you are currently viewing your design in.
• Design Position - click on the blue arrows to specify where the original design content sits within the new document size.
Tip: When the borders are added to the document, they are adding in the background colour set the Tools Palette. If you want your new borders to adopt a colour from the original artwork, set this colour as the background colour by using the Pipette Tool to ⌥ (option key) click on that colour. That colour will appear in the Tools Palette, and your new borders will be applied in that colour.