Sometimes annotations made on a Windows device are not visible on an iOS or Android device.
This problem is largely due to the fact that the native readers available on these platforms do not implement the PDF specification correctly. In addition, unfortunately native readers are used by many other app developers as an easy way to view PDFs, and so their software will suffer from this same issue.
To work around this limitation of other applications, you can flatten your annotations to the body of the document prior to sharing.
Learn to flatten PDFs from our guide: How to flatten form fields and annotations