Straight to your questions.
The project which you sent to us for your other question helped answering this one too.
To remove the boarder around the document pane and the header you have to remove the RadPaneGroup in which the Document Host was. Also after removing the Margin of the canvas (which was set to 25) the picture will be looking better.
Attached you will find your project with the above-mentioned changes.
Please let us know if that worked for you. If you have further question please feel free to contact us again.
the Telerik team