Which version of the projectdoc Toolbox is compatible to which version of Confluence can be easily determined on Version history page for the projectdoc Toolbox on the Atlassian Marketplace.
Installation
Go to Add-on Management
As an administrator of the Confluence server, click on the cog symbol and select Add-ons from the pulldown menu.
Find the projectdoc Toolbox on the Atlassian Marketplace
Click on the Find new add-ons link.
In the search field Search the Marketplace
enter projectdoc Toolbox and hit the return.
Install the projectdoc Toolbox
Choose between Free trial or Buy now and follow the instructions.