We tried to reproduce the issue “Custom stamp is not added in the PDF Viewer” in Xamarin.Forms, but it is working fine as expected. Kindly refer the sample in the below link which we created to reproduce the reported issue.
Kindly share the following details to analyze more on this issue and it will be helpful for us to analyze more on this issue.
1. Modify / Simple sample with which the issue could be reproduced.
2. Replication procedure to reproduce the issue or screen shot illustrating the issue.
3. Android / iOS device specification with the OS version.
4. Input Image with which the issue could be reproduced