The free DWGsign Reader checks any signatures (watermarks) previously to the current DWG document using the full commercial version of this add-on - DWGsign. Please note that the added watermark signature does not prove unmodified state of the original document (like digital signature does), it proves that a document is based on your original data. 

This application is compatible with the AutoCAD® 2015 and 2016 and 2017 families (32-/64-bit, any language version).

The installer that ran when you downloaded this plug-in from Autodesk Exchange Apps has already installed the plug-in. You may need to restart the Autodesk product to activate the plug-in. To uninstall this plug-in, click Control Panel > Programs > Programs and Features (Windows 7/8/8.1) or Control Panel > Add or Remove Programs (Windows XP), and uninstall as you would any other application from your system.