
<!-- note that this need to be placed in a section of Javascript within the page -->

var defaultHiddenFieldNameValue = ""; 

function getQueryStringParamValue(strQStrParam) { 

var strURL = document.location.href; 

var strQStrParamValue = ""; 

           if (strURL.indexOf('?') != -1)
           {
                       strQStrParamValue = strURL.substr(strURL.indexOf('?') + 1);
                       if (strQStrParamValue.indexOf(strQStrParam) != -1)
                       {
                                   strQStrParamValue = strQStrParamValue.substr(strQStrParamValue.indexOf(strQStrParam));
                                   strQStrParamValue = strQStrParamValue.substr(strQStrParamValue.indexOf('=') + 1);
                                   if (strQStrParamValue.indexOf('&') != -1)
                                   strQStrParamValue = strQStrParamValue.substr(0, strQStrParamValue.indexOf('&'));
                                   return strQStrParamValue;

                       }else{
                                   strQStrParamValue = defaultHiddenFieldNameValue;
                                   return strQStrParamValue;
                       }
           }else{
                       strQStrParamValue = defaultHiddenFieldNameValue;
                       return strQStrParamValue;
           }
} 

// Form name goes here 

var form = "WhitepaperForm_data"; 

function setCampaign(){ 

  var elqForm = document.forms[form];

  //repeat for each field to populate
  elqForm.elements['Campaign_ID'].value = getQueryStringParamValue('c');
} 

window.onload = setCampaign; 

<!-- note that this need to be placed in a section of Javascript within the page -->