Document OpenDocumentWithWorksets(Application app, ModelPath projectPath)
{
    Document doc = null;
    try
    {
        // Get info on all the user worksets in the project prior to opening
        IList<WorksetPreview> worksets = WorksharingUtils.GetUserWorksetInfo(projectPath);
        IList<WorksetId> worksetIds = new List<WorksetId>();
        // Find two predetermined worksets
        foreach (WorksetPreview worksetPrev in worksets)
        {
            if (worksetPrev.Name.CompareTo("Workset1") == 0 ||
                worksetPrev.Name.CompareTo("Workset2") == 0)
            {
                worksetIds.Add(worksetPrev.Id);
            }
        }

        OpenOptions openOptions = new OpenOptions();
        // Setup config to close all worksets by default
        WorksetConfiguration openConfig = new WorksetConfiguration(WorksetConfigurationOption.CloseAllWorksets);
        // Set list of worksets for opening 
        openConfig.Open(worksetIds);
        openOptions.SetOpenWorksetsConfiguration(openConfig);
        doc = app.OpenDocumentFile(projectPath, openOptions);
    }
    catch (Exception e)
    {
        TaskDialog.Show("Open File Failed", e.Message);
    }

    return doc;
}

Private Function OpenDocumentWithWorksets(app As Application, projectPath As ModelPath) As Document
    Dim doc As Document = Nothing
    Try
        ' Get info on all the user worksets in the project prior to opening
        Dim worksets As IList(Of WorksetPreview) = WorksharingUtils.GetUserWorksetInfo(projectPath)
        Dim worksetIds As IList(Of WorksetId) = New List(Of WorksetId)()
        ' Find two predetermined worksets
        For Each worksetPrev As WorksetPreview In worksets
            If worksetPrev.Name.CompareTo("Workset1") = 0 OrElse worksetPrev.Name.CompareTo("Workset2") = 0 Then
                worksetIds.Add(worksetPrev.Id)
            End If
        Next

        Dim openOptions As New OpenOptions()
        ' Setup config to close all worksets by default
        Dim openConfig As New WorksetConfiguration(WorksetConfigurationOption.CloseAllWorksets)
        ' Set list of worksets for opening 
        openConfig.Open(worksetIds)
        openOptions.SetOpenWorksetsConfiguration(openConfig)
        doc = app.OpenDocumentFile(projectPath, openOptions)
    Catch e As Exception
        TaskDialog.Show("Open File Failed", e.Message)
    End Try

    Return doc
End Function