To save document user data your plugin must override three
CRhinoPlugIn base class functions:
When Rhino writes a .3dm file, it goes through all the plugins that are currently loaded. First Rhino calls
CallWriteDocument() to see if the plugin wants to save document user data. If
true , Rhino saves information that identifies the plugin and then calls
WriteDocument() when it is time for the plugin to save its document user data.
When Rhino reads a .3dm file and it encounters document user data, it uses the plugin identification information (e.g. GUID) to load the plugin and then calls the plugin’s
ReadDocument() to read the plugin’s document user data.
Given this, does the plug-in you are working have the same plug-in ID as the one that originally wrote the document user text back in 2004?