How to change of item or file url in sharepoint 2010 document library.

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C#

SharePoint

Hi,
I am working on changing the item url of sharepoint 2010 document library programatically. Once user click on a document in the library the document should redirect to the NewItemURL, for this I have written the below code but its not giving the expected result. Could somebody please help me out on this.
string oldItemURL = item.Web.Url + "/" + item.File.Url;
string NewItemURL = "/Sites/MyTestSite/_layouts/MyCustomApplicationPage/MyCustomApplicationPage.aspx?ItemId=" + docID;
item.Url.Replace(oldItemURL, NewItemURL);
item.Update();