Hi @Dr Atul - LNG  I am writing this script on on change client script. This is working but when we save the form or submit the valid to is still changing and getting the form saved.

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
if (isLoading || newValue === '') {
return;
}

var validityField = 'valid_to';
   var onYearValidity = new Date(new Date().setFullYear(new Date().getFullYear() + 1));
var newValidity = new Date(newValue);

   if(newValidity > onYearValidity) {
      // g_form.clearValue(validityField);
       g_form.showErrorBox(validityField,'Valid to date must be within a year from today');
   } else {
       g_form.hideErrorBox(validityField);
   }

}

Thank you @Dr Atul - LNG  for your assistance, i am also posting this as one more question with code. Thank you very much for extending the help.

Please see the script I posted on the other post you submitted - https://www.servicenow.com/community/developer-forum/restrict-knowledge-article-valid-to-field/td-p/...