Digital Signature not working in PDF using Javascript

Hi,

I am trying to use a digital signature in adobe lifecycle using a javascript code using the .pfx file.

Here, I am attaching my demo code it's not working,

facing issues this,getField is not a function.

Code:-

 var myEngine = security.getHandler( "Adobe.PPKLite" );
myEngine.login( "123456", "/f/Bishal.pfx" );
var f = this.getField( "SignatureField1" );
var s = { reason: "I am the author of this document",
mdp: "allowNone" };
f.signatureSign({
oSig: myEngine,
oInfo: s,
bUI: false,
cLegalAttest: "Fonts are not embedded to reduce file size"
});

Please help me to solve this issue, thanks in advance.