Thanks for providing the required details.
We are able to reproduce the issue related to “Download as PDF” at our end. As the issue is specific to the front end application, therefore, we have logged it in our GitHub issues as: https://github.com/groupdocs-viewer/GroupDocs.Viewer-for-.NET-WebForms-App/issues/53. We will further look into it and keep you informed in case of any updates.
Furthermore, we are unable to reproduce the scrolling issue you mentioned in the screenshots. The file is rendering without any scrollbars in image view in Internet Explorer as well as in Google Chrome (see screenshot). Would you please share with us the version of Internet Explorer you are using at your end?
We can not find any issue regarding the thumbnails and render blank (see screenshot of thumbnails). Would you please share some more details on it?