You can only do this in Acrobat Pro.
If you have this, this is how you do it:
If your page is big enough, and already has the blue and green boxes around the outside where the marks should be, then it could be as simple process of just going Tools – Print Production (if this tab is not there go to the drop down menu at the top right of the tools panel to reveal it), then click the add Printer marks, you can then add the cropmarks, bleed etc in there, and when you click OK, job done. But its not always as easy as that. If that doesnt work, you will then need to set the crop boxes manually as below
First make sure that your page is bigger enough to accomodate the crop marks. If not, you will need to increase the page size, you can do this in the same dialogue from where you set the boxes.
Go to the Print Production tab and choose 'Set page boxes'.
Your page size needs to be big enough, so if its not, first change the page size manually at the bottom, then if you just want the crop marks, this is all you need to do, then click Ok, and return to the 'Add Printer marks', then select the marks that you want included and click 'OK'
If you want to add bleed marks which could be a requirement, these need to be configured in the 'Set Page Boxes
Hope this helps?