public override string Execute()
{
#if WEB
	_tpl.SetParameters(this);
#endif
	if (Width <= 0 || Height < 0)
	{
		ShowError("Invalid Width or Height");
		return null;
	}

	if (ConversionDelay < 0)
	{
		ShowError("Invalid conversion delay");
		return null;
	}

	// Set output path.
	var outputPath = Path.Combine(OutputDir, this.GetType().Name + ".pdf");
	if (File.Exists(outputPath))
		File.Delete(outputPath);

	// Create a new converter.
	var c = new HtmlToPdfConverter()
	{
		ViewportWidth = Width,
		ViewportHeight = Height,
		PageSize = PageSize,
		PageMargin = Margin,
		Portrait = Portrait,
		Delay = ConversionDelay,
		Timeout = Timeout,

		SinglePage = SinglePage
	};

	if (Progress != null)
		c.Progress += Progress;

	try
	{
		if (ConvertUrl)
		{
			if (string.IsNullOrWhiteSpace(Url))
			{
				ShowError("Please specify the URL to convert.");
				return null;
			}

			// Convert URL
			c.Convert(Url, outputPath);
		}
		else
		{
			if (string.IsNullOrWhiteSpace(HtmlString))
			{
				ShowError("Please specify the HTML string to convert.");
				return null;
			}

			// Convert the specified HTML string.
			c.ConvertString(HtmlString, HtmlStringBaseUrl, outputPath);
		}
	}
	catch (Exception ex)
	{
		ShowError(ex.Message);
	}

	return outputPath;
}