Hi Nishanth, a Document Choice Document (or DCD) allows the user to select which document to use from a list. This could be a list of template document, e.g. MS word files, or it could be a list of sourcing events. The advantage of DCD's are that you can link your review, approval etc. tasks to the one DCD on the template, rather than having to create conditional elements and multiple tasks for each possible document selection.
Hope that makes sense.
Cheers,
Ben