Download the appropriate installation file and run from any SharePoint Web Front End (WFE) server.
Select the Highlighter button to install, you may wish to also install the License Manager at the same time.
The automatic installer will verify some prerequisites (such as the SharePoint administration service is running) and if everything is ok will Install and Deploy the software to all Web Front End servers in your farm.
To remove the web part you can run the installer again and you will be given the option to remove.
Highlighter is a Custom Column and Custom Columns are classed as Farm Solutions in SharePoint so will not appear as Site Features.
If you want to check that Highlighter has installed and deployed look under: System Settings > Farm Management > Manage Farm Solutions. If you see it there marked as deployed, then when you create a new column on a list you will get the option of setting the type to Pentalogic Highlighter. See the Quick Start guide for more details.
The System Check shows "The SharePoint Administration service is NOT started!"
To install solutions to SharePoint the administration service must be running. Run services.msc and ensure that the following service is running then click Abort and try again.
SharePoint 2007 - Windows SharePoint Services Administration service
SharePoint 2010 - SharePoint 2010 Administration service
SharePoint 2013 - SharePoint 2013 Administration service
SharePoint 2016 & 2019 - SharePoint Administration service