You have several options:

1.  Loop all elements and set the respective protections
2. Disable the respective tools  - for example the following code disables the Move tool:

NTool tool = drawingView.Controller.Tools.GetToolByName(NDWFR.ToolMove);
tool.Enabled = false;

3. One dirty trick to disable modifcations is to set an invalid id to the ActiveLayerUniqueId property:
m_View.document.ActiveLayerUniqueId = Guid.NewGuid()

Tools that modify the document always take the active layer into account. If you do not have an active layer, user cannot modify or select anything.

Best Regards,
Nevron Support Team