Thank you for contacting Syncfusion support.
At present, we do support to draw only jpeg images in to the PDF document, so the exception occurs when drawing the TIFF image. Currently we do not have any solution to convert TIFF images to JPEG since Xamarin forms does not have native support for TIFF images, we have already logged a feature request for drawing TIFF image to PDF document in Xamarin platform. We will implement this feature in any of our upcoming releases. We usually have an interval of at least three months between releases. The feature implementation would also greatly depend on the factors such as product design, code compatibility and complexity. Please log on to our support website to check for further updates:
Please let us know if you need further assistance.