In PDFView.m, vopen() method, you can choose between two types of horizontal mode (left horizontal or right horizontal):

case 3:
  //for dual view

  //m_view = [[PDFVDual alloc] init:false :NULL :0 :NULL :0];
  //doublePage:YES;

  //for single view
  m_view = [[PDFVDual alloc] init:false :NULL :0 :verts :m_doc.pageCount];

  doublePage:NO;  
  break;

case 4:
  //for dual view

  m_view = [[PDFVDual alloc] init:true :NULL :0 :NULL :0];
  doublePage:YES;

  //for single view
  //m_view = [[PDFVDual alloc] init:true :NULL :0 :verts :m_doc.pageCount];

  //doublePage:NO; 
break;

You have to uncomment the command line that you’re looking for: for dual view or for single view.