public async Task RedactPdfWithRegexAsync(string inputFilePath, string outputFilePath)
{
    using var client = new HttpClient();

    // Set Authentication Header
    client.DefaultRequestHeaders.Authorization =
        new AuthenticationHeaderValue("Bearer", "YOUR_API_KEY");

    using var form = new MultipartFormDataContent();

    // Redaction configuration with EMAIL, SSN, and custom Regex
    var redactionConfigJson = @"{
        ""types"": [""EMAIL_ADDRESS"", ""SSN""],
        ""regex"": [""\\b\\d{3}-\\d{2}-\\d{4}\\b""]
    }";

    form.Add(new StringContent(redactionConfigJson), "redaction_config");

    // Prepare file: must use "file:fileName" format as per Swagger
    byte[] fileBytes = await File.ReadAllBytesAsync(inputFilePath);
    var fileContent = new ByteArrayContent(fileBytes);
    fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse("application/pdf");

    string fileName = Path.GetFileName(inputFilePath);
    form.Add(fileContent, "file", $"file:{fileName}");

    // Execute Synchronous POST
    var response = await client.PostAsync("https://services.forecastica.com/aws/api/pdf/redact", form);

    if (response.IsSuccessStatusCode)
    {
        byte[] redactedPdf = await response.Content.ReadAsByteArrayAsync();
        await File.WriteAllBytesAsync(outputFilePath, redactedPdf);
    }
}