Getting 401 Error (Unathorised error) when accessing document library in Sharepoint 2013

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C#

SharePoint2013

Through provider hosted app for Sharepoint 2013, I am accessing doc lib document and copying that content to a new document and uploading it into doclib.


Getting 401 error at ---ClientOM.File.OpenBinaryDirect(clientContext, (string)listItem["FileRef"]);

Page_Load method:
var spContext = SharePointContextProvider.Current.GetSharePointContext(Context);

MemoryStream memStream = new MemoryStream();



using (var clientContext = spContext.CreateAppOnlyClientContextForSPHost())
{

List docLib = clientContext.Web.Lists.GetByTitle("TestDocLib");
ClientOM.ListItem listItem = docLib.GetItemById(1);

clientContext.Load(docLib);
clientContext.Load(docLib.RootFolder);
clientContext.Load(listItem);
clientContext.ExecuteQuery();


try
{
FileInformation fileInformation = ClientOM.File.OpenBinaryDirect(clientContext, (string)listItem["FileRef"]);

CopyStream(fileInformation.Stream, memStream);


string serverRelativeUrl = docLib.RootFolder.ServerRelativeUrl + "/test1.docx";


memStream.Seek(0, SeekOrigin.Begin);
ClientOM.File.SaveBinaryDirect(clientContext,
serverRelativeUrl, memStream, true);
}



catch (Exception exp)
{

}

}