Tady v té funkci

private string jmenoPGM(string jmeno)
{
jmeno = "0 BEGIN PGM " + txtJmenoPGM.Text + " MM"
+ Environment.NewLine + Environment.NewLine +
"150 END PGM " + txtJmenoPGM.Text + " MM";
return jmeno;
}

Tak to funguje

public string JmenoPGM
{
get
{
return "0 BEGIN PGM " + txtJmenoPGM.Text + " MM"
+ Environment.NewLine + Environment.NewLine +
"150 END PGM " + txtJmenoPGM.Text + " MM";
}