This helper method will do it.
-(PTPDFRect*)CGRectScreen2PDFRectPage:(CGRect)cgRect PageNumber:(int)pageNumber
{
CGPoint topLeft = cgRect.origin;
CGPoint bottomRight = CGPointMake(CGRectGetMaxX(cgRect), CGRectGetMaxY(cgRect));
[self ConvertScreenPtToPagePtX:&topLeft.x Y:&topLeft.y PageNumber:pageNumber];
[self ConvertScreenPtToPagePtX:&bottomRight.x Y:&bottomRight.y PageNumber:pageNumber];
PTPDFRect* ptRect = [[PTPDFRect alloc] initWithX1:topLeft.x y1:topLeft.y x2:bottomRight.x y2:bottomRight.y];
[ptRect Normalize];
return ptRect;
}
-(void)ConvertScreenPtToPagePtX:(CGFloat*)x Y:(CGFloat*)y PageNumber:(int)pageNumber
{
[m_screenPt setX:*x];
[m_screenPt setY:*y];
m_pagePt = [m_pdfViewCtrl ConvScreenPtToPagePt:m_screenPt page_num:pageNumber];
*x = (float)[m_pagePt getX];
*y = (float)[m_pagePt getY];
}