You may be able to, but only if your administrator has set up a field that supports file attachments on your timesheet, time off booking, or project. If they have, the field will be located:

• For projects, at the bottom of the Project Info dialog
• For timesheets, in custom fields above or below your timesheet grid
• For time off bookings, in a field that displays once you've selected a time off type

Attaching files can be useful if your timesheet or time off booking requires supporting documentation