Thanks for considering Aspose.
Aspose.Pdf.Kit is a component which is used to manipulate/edit existing PDF documents. As per your requirements, I am pleased to inform you that Aspose.Pdf.Kit offers the capability to rotate the pages of existing PDF documents but I am afraid it does not allow the feature to save the changes in original document. You need to save the updated document as separate file. Please try using the following code snippet and in case you encounter any problem or you have any further query, please feel free to contact.
// create PDF page editor object
PdfPageEditor editor = new PdfPageEditor();
// bind the source PDF document over which you need to perform operations
// specify the page roration value
editor.Rotation = 90;
// after the modifcations have been applied, save the document as new file
For more related information, please visit PdfPageEditor and PdfPageEditor Members.