When using a docx file with ticked checkboxes, they are not displayed as ticked on the webviewer.
You can test it by downloading the test file below or by creating a docx file with ticked checkbox and by uploading it on the PDFTRON demo : https://www.pdftron.com/webviewer/demo/
This issue has now been fixed and can be found in our nightly builds as well as our upcoming 8.2 release.
Here is a link to the nightly builds: PDFTron Systems Inc. | Nightly