Checking off pdf checkbox with itextsharp -

i've tried many different ways, can't check box checked! here's i've tried:

var reader = new itextsharp.text.pdf.pdfreader(originalformlocation); using (var stamper = new itextsharp.text.pdf.pdfstamper(reader,ms)) {     var formfields = stamper.acrofields;     formfields.setfield("isno", "1");     formfields.setfield("isno", "true");     formfields.setfield("isno", "on"); } 

none of them work. ideas?

you shouldn't "guess" possible values. need use value stored in pdf. try checkboxvalues example find these possible values:

public string getcheckboxvalue(string src, string name) throws ioexception {     pdfreader reader = new pdfreader(src);     acrofields fields = reader.getacrofields();     // cp_1 name of check box field     string[] values = fields.getappearancestates("isno");     stringbuffer sb = new stringbuffer();     (string value : values) {         sb.append(value);         sb.append('\n');     }     return sb.tostring(); } 

or take @ pdf using rups. go widget annotation , normal (/n) appearance (ap) states. in example /off , /yes: