The spec for this action:
https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#G11.2111850
An example of a form using this action:
https://www2.illinois.gov/rev/forms/reg/Documents/reg-1-mr.pdf
case "Named":
          const namedAction = action.get("N");
          if (isName(namedAction)) {
            resultObj.action = namedAction.name;
          }
          break;
        case "JavaScript":
          const jsAction = action.get("JS");
          let js;
          if (isStream(jsAction)) {
            js = jsAction.getString();
          } else if (isString(jsAction)) {
            js = jsAction;
          }
          const jsURL = js && recoverJsURL(stringToPDFString(js));
          if (jsURL) {
            url = jsURL.url;
            resultObj.newWindow = jsURL.newWindow;
            break;
          }
        
        default:
          if (
            actionName === "JavaScript" ||
            actionName === "ResetForm" ||
            actionName === "SubmitForm"
          ) {
            
            
            break;