I faced the same issue , to resolve it we have to manually start the exe process in code.
{
var _wkHtmlToPdfPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Configuration/wkhtmltopdf/wkhtmltopdf.exe");
var pdfBytes = new byte[0];
var arguments = $"--page-size A4 --encoding utf-8 - -";
using (var process = new Process())
{
process.StartInfo.FileName = _wkHtmlToPdfPath;
process.StartInfo.Arguments = arguments;
process.StartInfo.UseShellExecute = false;
process.StartInfo.RedirectStandardInput = true;
process.StartInfo.RedirectStandardOutput = true;
process.StartInfo.RedirectStandardError = true;
process.StartInfo.CreateNoWindow = true;
process.Start();
using (var streamWriter = new StreamWriter(process.StandardInput.BaseStream))
{
streamWriter.Write(htmlBody);
}
using (var memoryStream = new MemoryStream())
{
process.StandardOutput.BaseStream.CopyTo(memoryStream);
pdfBytes = memoryStream.ToArray();
}
process.WaitForExit();
process.Close();
}