This documentation is not using the current rendering mechanism and will be deleted by December 31st, 2020. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
The following chapter provides guides to upgrade from one major version to the next major version. This includes only breaking changes, for a complete changelog please see https://github.com/bithost-gmbh/pdfviewhelpers/blob/master/CHANGELOG.md . If there is something missing in one of these guides please tell us via mail, a GitHub issue or even better a pull request!