By default users are able turn to a page by clicking once on any of the page corners. To control this behaviour you can use the PageFlipMode property. It is an enumeration that contains the following values:
None - this will disable the flip mode by user click
SingleClick - this is the default value. The page flip will happen on single click
DoubleClick - the page flip will happen on double click.
<telerik:RadBook Margin="50" x:Name="RadBook1" PageFlipMode="DoubleClick">