Unable to cast object of type 'Newtonsoft.Json.Linq.JObject' to type 'Newtonsoft.Json.Linq.JArray'

Just make a class and deserialize it.

public class Print
{
    public int PrintId { get; set; }
    public string Header { get; set; }
    public string TC { get; set; }
    public string CompanyRef { get; set; }
}

Print printObj = JsonConvert.DeserializeObject<Print>(yourJson);
printObj.PrintId = //...

As the message says, your object is JObject so don't cast it to JArray. Try this:

var objs = JsonConvert.DeserializeObject("{ \"PrintId\":10,\"Header\":\"header\",\"TC\":\"tc\",\"CompanyRef\":\"00000000-0000-0000-0000-000000000000\"}");

Update To get a collection List<Print>, your JSON needs to be an array. Try this (I made your JSON an array and added a second object):

string json = "[{ \"PrintId\":10,\"Header\":\"header\",\"TC\":\"tc\",\"CompanyRef\":\"00000000-0000-0000-0000-000000000000\"}"
            + ",{ \"PrintId\":20,\"Header\":\"header2\",\"TC\":\"tc2\",\"CompanyRef\":\"00000000-0000-0000-0000-000000000000\"}]";
var objs = JsonConvert.DeserializeObject<List<Print>>(json);

//The loop is only for testing. Replace it with your code.
foreach(Print p in objs){
    Console.WriteLine("PrintId: " + p.PrintId);
    Console.WriteLine("Header: " + p.Header);
    Console.WriteLine("TC: " + p.TC);
    Console.WriteLine("CompanyRef: " + p.CompanyRef);
    Console.WriteLine("==============================");
}

public class Print
{
    public int PrintId { get; set; }
    public string Header { get; set; }
    public string TC { get; set; }
    public string CompanyRef { get; set; }
}

Here is a fiddle.