Problem
After exporting a document to a PDF, some or all images in it might be missing when viewed in specific PDF viewers or web browsers.
The file format Goodnotes uses to store image information is JPEG2000. This format has the benefits of a small file size, while also supporting transparency like PNG.
The problem is that some PDF viewers do not support JPEG2000 and therefore can't display the images, while others can.
Workaround
While we're working on a solution to introduce better compatibility, you can open the PDF in macOS Preview (if on a Mac), press command+P and then choose "Save As PDF." Then, the images in the new PDF should be properly displayed in other PDF viewers as well. If you don't have a Mac, you can try using Chrome to print the problematic PDF to a new one.