There have been lots of issues in regards to DRM plugin – file protected, locked etc. One of the best thing you can do is by updating the DRM plugin to resolve the issue.

Please check this link to download the latest version (April 2020) of DeDRM plugin.

For those who are unsure how this works, please check our earlier tutorial video – “Convert Kindle Books to PDF using free software?” You can directly follow the steps as in this earlier video and skip this tutorial because you can install the updated version of DeDRM.

Hope it helps.