How do I add Annotations in the existing PDF through C#?

Hi,

I m trying to add the rectangle annotation to the existing PDF but not able to achieve that.Please help to solve this. I m using Adobe Acrobat 9 pro. I tried with the below C# code,

string inputfilepath="C:\\RedLine.pdf"

//Object for Adobe application and Document

AcroApp gApp;

AcroAVDoc acroAVDoc;

//Initialize Acrobat Application

gApp = new AcroApp();

//Open PDf Document

acroAVDoc = new AcroAVDoc();

acroAVDoc.Open(inputfilepath, "output");

//To show the Application

gApp.Show();

CAcroPDDoc acroPDDoc = (CAcroPDDoc)acroAVDoc.GetPDDoc();

//Rectangle bounds

AcroRect acroRect = new AcroRect();

acroRect.Left = 906;

acroRect.right = 815;

acroRect.Top = 377;

acroRect.bottom = 142;

CAcroPDAnnot acroPDAnnot = acroPDPage.AddNewAnnot(2, "Rectangle", acroRect);

acroPDAnnot.SetContents("Testing the Acrobat Redline");

Thanks in advance,

SASIKUMAR