public Task CopyFile(string fileName, string targetPath)
{
    var blobRef = Container.GetBlockBlobReference(targetPath);

    blobRef.Properties.ContentType = GetContentType(fileName);

    return blobRef.UploadFromFileAsync(fileName);
}

public string GetContentType(string fileName)
{
    var provider = new FileExtensionContentTypeProvider();

    if (!provider.TryGetContentType(fileName, out var contentType))
    {
        contentType = "application/octet-stream";
    }

    return contentType;
}

<Error>
    <Code>ResourceNotFound</Code>
    <Message>
        The specified resource does not exist. RequestId:12485818-601e-0017-6f69-56c3df000000 Time:2019-08-19T08:35:13.2123849Z
    </Message>
</Error>