Hi Scott,
Thank you for using Syncfusion products.
Issue 1:
The best method to insert an image is by using the Insert method in the PDFDocument object. Template will not be the best way to insert a single image to a PDF document. It will be effective only when inserting images to more number for pages. Here is the sample to insert an image(*.bmp) in an existing PDF document.
http://websamples.syncfusion.com/samples/PDF.Windows/F_59154/main.htmIssue 2:
Regarding the performance of the inserting many number of images in an existing PDF, can you please create an Direct Trac incident, so that I can update the details regarding this in the Incident.
Please let me know if you face any issues.
Regards,
Sarath