HTTP Server error 500 is usually caused by some issue in software on your site/server. There are plenty of reasons why this error could appear. To fix it we’ll need to know the error exactly.

You can find the error description in the your site/server’s log files. Here is some basic instruction on how to find logs on your server with cPanel example

Also you can use wordpress log, if you’re not familiar with it please check the following article:

Also will be useful to send us PDF Light Viewer log, which could be found on the settings page /wp-admin/options-general.php?page=pdf-light-viewer

Please send your site/server’s error log to us, so we could advise how to solve the issue or fix it if the issue in our plugin.

Warningthe log file contains sensitive data of your server which you don’t want to share with the world. So please send your site/server’s error log in the direct email and don’t publish it publicly anywhere.