interface IAppxEncryptedPackageWriter : public IUnknown
{
public:
    virtual HRESULT STDMETHODCALLTYPE AddPayloadFile(
        /* [string][in] */ __RPC__in_string LPCWSTR fileName,
        /* [string][in] */ __RPC__in_string LPCWSTR contentType,
        /* [in] */ UINT64 compressedSize,
        /* [in] */ UINT64 uncompressedSize,
        /* [in] */ __RPC__in_opt IStream *inputStream,
        /* [in] */ __RPC__in_opt IUri *contentId) = 0;

    virtual HRESULT STDMETHODCALLTYPE Close( void) = 0;
};

#include <appxpackaging.h>

// Assume you have an IAppxEncryptedPackageWriter* named encryptedPackageWriter

LPCWSTR fileName = L"example.txt";
LPCWSTR contentType = L"text/plain";
UINT64 compressedSize = /* compressed size */;
UINT64 uncompressedSize = /* uncompressed size */;
IStream* inputStream = /* input stream for the file */;
IUri* contentId = /* content identifier for the file */;

// Add a payload file to the encrypted package
HRESULT hr = encryptedPackageWriter->AddPayloadFile(
    fileName, contentType, compressedSize, uncompressedSize, inputStream, contentId);

if (SUCCEEDED(hr)) {
    // The file was added successfully
}

// Close the encrypted package writer
hr = encryptedPackageWriter->Close();
if (SUCCEEDED(hr)) {
    // The package writer was closed successfully
}