Convert DOCX to DOC | DOC to DOCX Programmatically using C++ | https://blog.aspose.com/2021/06/28/convert-docx-to-doc-or-doc-to-docx-using-cpp/

01_Convert_DOCX_to_DOC_or_DOC_to_DOCX_using_CPP

Read the complete article about converting DOCX to DOC or DOC to DOCX programmatically using C++ by visiting the following link.
https://blog.aspose.com/2021/06/28/convert-docx-to-doc-or-doc-to-docx-using-cpp/

Convert-DOC-to-DOCX-Batch.cpp

// Iterate through the files in the directory
for (directory_entry& file : directory_iterator("SourceDirectory\\Word"))
{
    // Check file extension
    if (file.path().extension().string() == ".doc")
    {
        // Create an instance of the LoadOptions class
        auto loadOptions = System::MakeObject<LoadOptions>();

        // Specify LoadFormat of input word document
        loadOptions->set_LoadFormat(LoadFormat::Doc);

        // Load the DOC file
        System::SharedPtr<Document> doc = System::MakeObject<Document>((System::String)file.path().string(), loadOptions);

        // Change the file extension
        System::String fileName = (System::String)file.path().filename().string();
        fileName = fileName.Replace(u".doc", u".docx");

        // Save the DOCX file
        doc->Save(System::String::Concat(u"OutputDirectory\\", fileName), SaveFormat::Docx);
    }
}

Convert-DOC-to-DOCX.cpp

// Create an instance of the LoadOptions class
auto loadOptions = System::MakeObject<LoadOptions>();

// Specify LoadFormat of input word document
loadOptions->set_LoadFormat(LoadFormat::Doc);

// Load source DOC file
System::SharedPtr<Document> doc = System::MakeObject<Document>(u"SourceDirectory\\Word\\Sample 1.doc", loadOptions);

// Save the DOCX file
doc->Save(u"OutputDirectory\\output.docx", SaveFormat::Docx);

Convert-DOCX-to-DOC-Batch.cpp

// Iterate through the files in the directory
for (directory_entry& file : directory_iterator("SourceDirectory\\Word"))
{
    // Check file extension
    if (file.path().extension().string() == ".docx")
    {
        // Create an instance of the LoadOptions class
        auto loadOptions = System::MakeObject<LoadOptions>();

        // Specify LoadFormat of input word document
        loadOptions->set_LoadFormat(LoadFormat::Docx);

        // Load the DOCX file
        System::SharedPtr<Document> doc = System::MakeObject<Document>((System::String)file.path().string(), loadOptions);

        // Change the file extension
        System::String fileName = (System::String)file.path().filename().string();
        fileName = fileName.Replace(u".docx", u".doc");

        // Save the DOC file
        doc->Save(System::String::Concat(u"OutputDirectory\\", fileName), SaveFormat::Doc);
    }
}

Convert-DOCX-to-DOC.cpp

// Create an instance of the LoadOptions class
auto loadOptions = System::MakeObject<LoadOptions>();

// Specify LoadFormat of input word document
loadOptions->set_LoadFormat(LoadFormat::Docx);

// Load source DOCX file
System::SharedPtr<Document> doc = System::MakeObject<Document>(u"SourceDirectory\\Word\\Sample 4.docx", loadOptions);

// Save the DOC file
doc->Save(u"OutputDirectory\\output.doc", SaveFormat::Doc);