Why does a custom Stamp annotation lose its appearance after being resized?

Custom Stamp annotations rely on both an appearance and the original image data. The appearance is a rendered snapshot of how the stamp currently looks, while the image data is the original source image used to create that appearance. When a stamp is first loaded, WebViewer can display it using the appearance alone.

When a custom Stamp annotation is resized, moved, or otherwise modified, the existing appearance is discarded and a new appearance must be generated to reflect the updated annotation state. To regenerate the appearance, WebViewer needs access to the original image data. If the image data is unavailable, WebViewer cannot regenerate the appearance, causing the stamp image to disappear.

To prevent this issue, ensure that the stamp's image data is preserved when exporting and importing annotations. If the XFDF does not contain <imagedata>, the image can be restored after import by calling annotation.setImageData(...) before the annotation is edited. This allows WebViewer to regenerate the appearance whenever the annotation is updated.