PdfDocumentOptionsAutoResizePdfPageWidth Property

Automatically resizes the PDF page width to match the HtmlViewerWidth value at the default 96 DPI resolution. To obtain a PDF with the exact page size given by PdfPageSize, set the AutoResizePdfPageWidth and AutoResizePdfPageHeight properties to false. The default value is true

public bool AutoResizePdfPageWidth { get; set; }