如何在使用cgpdfdocumentref ...渲染时将pdf与屏幕尺寸相匹配？

I am new to ipad application development. I am rendering a pdf book using CGPDFDocumentRef in the iPad. I am able to render the pdf properly which is coming in the centre of the page. Its leaving small length of white space on all the sides. I am trying to scale that image which we are getting in centre to fit the page exactly...can any one help me out how to make that fit into the ipad screen size?I am new to ipad application development. I am