set-adserverstettings -viewentireforrest:$true
    get-mailbox Administrator | fl

Name,Alias,ServerName,ProhibitSendQuota
    Administrator,admin,ex01,unlimited

var command = new Command("get-mailbox");
command.Parameters.Add("Identity", "Administrator");
pipeline.Commands.AddScript("Set-ADServerSettings -ViewEntireForest:$true");
pipeline.Commands.Add(command);

Nothing/EMPTY/NULL

pipeline.Commands.AddScript("Get-Mailbox -identity Administrator");

Administrator (Global Admin Account)

string runasUsername = "admin@abc.at";
string runasPassword = "MyPassword";

System.Security.SecureString ssRunasPassword = new System.Security.SecureString();

foreach (char x in runasPassword)
    ssRunasPassword.AppendChar(x);

PSCredential credentials = new PSCredential(runasUsername, ssRunasPassword);
var connInfo = new WSManConnectionInfo(new Uri("http://ex01.abc.at/PowerShell"), "http://schemas.microsoft.com/powershell/Microsoft.Exchange", credentials);
connInfo.AuthenticationMechanism = AuthenticationMechanism.Kerberos;

var runspace = RunspaceFactory.CreateRunspace(connInfo);

string script = @"Set-ADServerSettings -ViewEntireForest:$true
        get-mailbox Administrator | format-table";

runspace.Open();
var pipeline = runspace.CreatePipeline();

pipeline.Commands.AddScript(script);
Collection<PSObject> resultss = pipeline.Invoke();
string str = "";

foreach (PSObject psObject in resultss)
{
    str = str + psObject;
}

runspace.Dispose();
Label1.Text = str;