eDrawings markup API (such as comments, stamps, measurements) can be accessed via IEModelMarkupControl interface.

Interop can be found in the eDrawings installation folder: %commonprogramfiles%\eDrawings[Version]\eDrawings.Interop.EModelMarkupControl.dll

Markup interface can be accessed by calling the IEModelViewControl::CoCreateInstance eDrawings API method.

It is possible to pass both version specific and version independent GUID or ProgId of the markup control.

Version independent guid can be located in the registry HKEY_CLASSES_ROOT\EModelViewMarkup.EModelNonVersionSpecificMarkupControl\CLSID

Version independent eDrawings Markup control GUID
Version independent eDrawings Markup control GUID

Version specific guids can be located under the corresponding version of the markup control (e.g. EModelViewMarkup.EModelViewMarkupControl.18 for eDrawings 2018 or EModelViewMarkup.EModelViewMarkupControl.19 for eDrawings 2019)

//creating version independent instance of markup using prog id
var eDrawingsMarkupCtrl = eDrawingsCtrl.CoCreateInstance("EModelViewMarkup.EModelMarkupControl") as EModelMarkupControl;
...
//creating version independent instance of markup using guid
var eDrawingsMarkupCtrl = eDrawingsCtrl.CoCreateInstance("{5BBBC05A-BD4D-4e3b-AD5B-51A79DFC522F}") as EModelMarkupControl;
...
//creating version specific instance of markup (eDrawings 2018) using prog id
var eDrawingsMarkupCtrl = eDrawingsCtrl.CoCreateInstance("EModelViewMarkup.EModelMarkupControl.18") as EModelMarkupControl;