OpenXML SDK -Converting C# to C++/CLI -created file is corrupt and it cannot be opened

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C++

C++/CLI

C#

Hi,
I'm trying to write a simple hello world application in C++/CLI to create a Word document which I've posted below

int main(array<String^>^ args)
{
    String^ documentFileName=L"Hello4.docx";
    WordprocessingDocument ^myDoc = WordprocessingDocument::Create(documentFileName, WordprocessingDocumentType::Document);
    MainDocumentPart^ mainPart = myDoc->AddMainDocumentPart();
    mainPart->Document  = gcnew Document();
    Body^ body = gcnew Body();
    Paragraph^ paragraph = gcnew Paragraph();
    Run^ run_paragraph = gcnew Run();
    DocumentFormat::OpenXml::Wordprocessing::Text^ text_paragraph = gcnew DocumentFormat::OpenXml::Wordprocessing::Text(L"Hello ..asdks");
    run_paragraph->Append(text_paragraph);
    paragraph->Append(run_paragraph);
    body->Append(paragraph);
    mainPart->Document->Append(body);
    mainPart->Document->Save();
    return 0;
}

The above program creates hello.docx file but I'm not able to open the created file as it is corrupt.Can you please help me with this
Thanks in advance