missing response header in HEAD request when using HttpClient

Question

the following code

    var request = new HttpRequestMessage(HttpMethod.Head, url);
    var response = await client.SendAsync(request);
    Console.WriteLine(response.Headers);

prints the headers as

Server: Apache
Date: Fri, 11 Nov 2022 00:23:09 GMT
Accept-Ranges: bytes
ETag: "112a18-2120d2-5a3f75745e000"
Connection: Keep-Alive

but when using a generic HTTP test tool I see that the response also contains headers

Last-Modified: Thu, 23 Apr 2020 16:00:00 GMT
Content-Length: 2171090
Content-Type: application/pdf

How can one read the access the additional Headers, specifically Last-Modified ?

postman shows the complete list of 8 headers