End Text Editing and Save                 

You can end the ending mode at any time. You can use CPDFViewer's SetMouseMode to exit the editing mode. To save the changes of editing text, use WriteToLoadedPath or WriteToFilePath .

//Exit the editing mode to PanTool mode
viewer.SetMouseMode(MouseModes.PanTool);

if(viewer.UndoManager.CanSave)
{
  //save changes to local file
  viewer.Document.WriteToLoadedPath();
}