Thank you for your feedback and question. My apologies if it’s unclear. The source code for the UI is available on GitHub [1], but is minified in the download package for efficiency. Note that even though the code is "open source" in that repo, we still have a custom license [2]. [1] https://github.com/PDFTron/webviewer-ui [2] https://github.com/PDFTron/webviewer-ui/blob/6.2/LICENSE