ClientContext = new ClientContext(SharePointUrl);
ClientContext.Credentials = Credentials;
docUrl = docUrl.GetRelativeUrl(docUrl);
File file = ClientContext.Web.GetFileByServerRelativeUrl(docUrl);
ListItem item = file.ListItemAllFields;
ClientContext.Load(item, i => i.Id, i => i.File);
ClientContext.ExecuteQuery();

/sites/products/_layouts/DocIdRedir.aspx?ID=PRODUCTS-1-20239

string documentIdUrl = "https://***/_layouts/15/DocIdRedir.aspx?ID=FDQETV2AVKRD-2102554853-1";
HttpWebRequest request = WebRequest.CreateHttp(documentIdUrl);
request.UseDefaultCredentials = true;
request.AllowAutoRedirect = false;
WebResponse response = request.GetResponse();
Console.WriteLine(response.Headers["Location"]);