PDF Viewer writes annotations in accordance to the standardized PDF specification. Any compliant viewer (like Adobe Acrobat) will be able to display and edit such annotations and forms. Using standard compliant software, annotations can be created e.g. using PDF Viewer for iOS, edited in Adobe Acrobat for Windows and later displayed and edited/deleted on PDF Viewer for Android without any problems.

Apple's Preview app is only partly compliant to the PDF specification, therefore showing and editing PDF files in Preview, can sometimes lead to display issues or missing annotations. Documents that were annotated in PDF Viewer, and later edited using Preview, might look different when imported to PDF Viewer again.

You can read more about 3rd-party compatibility in the guides of the underlying PDF framework of PDF Viewer - PSPDFKit.

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