For professional printing, bleed extends the printable area beyond the page edge to allow artwork to be trimmed. You can set bleed on document setup, display bleed guides (so you can more easily design into the bleed area) and assign colors to them and then include bleed at print or export time.
To allow for inaccuracies in the trimming process in professional printing, it's a good idea to extend these elements beyond the 'trim edge' (TrimBox), i.e. the page dimensions defined in Document Setup.
Bleed guides are a visual aid only which assist you in positioning 'bleed' elements (typically images) that you want to run to the edge of a trimmed page. With bleed guides switched on, you can display the printable area extended by the Bleed distance you specify.
An Include bleed setting in the Export PDF or Print dialog includes the bleed in the actual output page size.
For single pages, the terms 'Left' and 'Right' bleed are used, while for facing-page spreads the terms 'Inner' and 'Outer' are used. For the latter, Inner bleed is only relevant for first and last single pages or when exporting (printing) as single pages (rather than spreads).
To set bleed for new documents:
From the File menu, click New.
Select the Bleed tab, and do one of the following:
For different bleed values at single-page edges (Facing pages unchecked): Set the Left, Right, Top, and Bottom bleed.
For different bleed values at two-page spread edges (Facing pages checked): Set the Inner, Outer, Top, and Bottom bleed.
For the same bleed value: Enable the Link symbol at right, and set any bleed value; all other values will update to this.
To modify your bleed settings:
From the default context toolbar (or File menu), select Document Setup.
Change bleed values from the Bleed tab.
To view bleed guides:
From the View menu, select Show Bleed.
The guides are shown as an outline that extends beyond the page edge by the chosen Bleed value.
To change the color of bleed guides:
From the File menu, select Document Setup.
Click the color swatch to display a pop-up panel to update the bleed color.
To snap objects to bleed guides:
From the main toolbar, enable Snapping, then click the Snapping down arrow and ensure Snap to Spread is checked.
The Snap to Spread option snaps to spread edge, page edge and bleed equally.
To preview your page without this design aid:
Do one of the following:
From the toolbar, ensure Toggle Preview Mode is selected.
From the View menu, select Preview Mode. Other on-screen design aids will also be disabled and clip to canvas is employed.
To switch on bleed marks on export:
Do one of the following:
For print: From the File menu, select Print. Click Show Details, then Bleed and Marks, and check Include bleed.
For print: From the File menu, select Print. Go to Bleed and Marks and check Include bleed.
For pro PDF output: From the File menu, select Export, then PDF. Choose any PDF/X Preset, then check Include bleed.