In order to import any type of custom extensions, you should have a full license to access the Denodo Platform which imposes that importing extensions (jars) is not allowed in Denodo express. You can look at the section [Limitations of Denodo Express](https://community.denodo.com/docs/html/browse/latest/platform/installation/appendix/limitations_of_the_denodo_express_license/limitations_of_the_denodo_express_license#limitations-of-the-denodo-express-license).
To obtain an unrestricted evaluation license for the Denodo Platform, please contact the appropriate Denodo Sales Representative for your region or organization.
You can contact ‘firstname.lastname@example.org’ or fill in a Contact Request at http://www.denodo.com/action/contact-us.
Once you have obtained your evaluation license, you will be able to upgrade your Denodo Express installation by downloading and applying the latest Denodo Update from the Denodo Support Site.
With this license you can download (from the Denodo Support Site), you will be able to use the full Denodo Platform including the HDFS custom wrapper for the evaluation period.
Hope this helps.