I have a requirement to perform a callout from an LWC to get invoices data and then display as a PDF the data returned. So i have an LWC with a lightning data table and on row action it calls an apex class to do the callout and get the result. In order to do the rendering to PDF, i created a visualforce page which is called from apex. However, i didn't manage to find solution i was getting several errors like "ERROR: Formula Expression is required on the action attributes." or like "common.apex.runtime.impl.executionexception argument cannot be null". Seems like i am doing something wrong when passing the data from Apex to the Visualforce.

so, the issue is:

  1. i have got the invoice data of structure:
public class el_invoices{
        public Boolean Success {get; set;}
        public String ErrorCode {get; set;}
        public String ErrorMessage {get; set;}
        public String BillNo {get; set;}
        public String BillData {get; set;}
  1. Then on specific invoice action i call from my LWC an APEX function showPDF
    public static void showPDF(String s){
        System.debug('in show pdf: '+s);
    public static blob navigate(String s) {
        PageReference pg = new PageReference('/apex/el_generatePDF');
        pg.getParameters().put('displayText', 'sdfsdf');
        //blob doccontent = pg.getContent();
        //ystem.debug('doccontent '+doccontent);
        system.debug('show pdf finish');
        return pg.getContent();
  1. But my visualforce is always blank, like i cannot pass data from my apex class to the "displayText" attribute. Has anyone found solution on such topic? Again, what i want is to make a callout, and show a PDF (not save anything in the database)
<!--<apex:page controller="el_generatePDFController" contentType="application/pdf" renderAs="pdf">-->
<apex:page controller="el_generatePDFController" contentType="application/pdf" renderAs="pdf">

    <apex:form >
        <!-- Page code -->
        <apex:inputhidden id="hidData" value="{!displayText}"/>
public with sharing class el_generatePDFController {
    public String displayText {get; set;}

    public String getdisplayText (){
        /*//System.debug('s: '+ s);
        System.debug('pdfdatastring: '+ pdfdatastring);
        return EncodingUtil.base64Decode(pdfdatastring).toString();
        displayText = 'giorgos';
        return displayText;

UDATE: I edit my question to show at a high level the problem that i am facing: enter image description here

1 Answer 1


You can't generate a form in the page that would be manipulated into rendering the PDF, because that would be a second round trip. You can either (a) put the content into a page parameter (maximum limit is about 3k characters), or, as I would recommend, use Blob.toPdf() to directly generate the PDF!

Here's a revised version of your method that should help:

public static blob navigate(String s) {
    return Blob.valueOf(s).toPDF();

Of course, you have some more work to do, but this should get you started. Just render a full, proper HTML document, pass it to your Apex method, and then you can render the PDF immediately.

  • Hi sfdcfox and thank you very much for your response! Could you please help me with what "render a full, proper HTML document" means? I should return my blob to the LWC? Or call a vf page passing the blob content as a parameter? I tried both but did not find solution. Jan 15, 2021 at 14:19
  • @GiorgosGalaios You don't need the VF page at all. Simply generate an HTML document, and call toPDF().
    – sfdcfox
    Jan 15, 2021 at 14:54
  • How could i generate an html document from lwc? You mean to reference a static resource? It is still not clear to me :( Jan 15, 2021 at 15:43
  • @GiorgosGalaios The string is literally HTML, such as <html><head><title>Report</title></head><body>...</body></html>, then passed in to Blob.valueOf, and then converted to a PDF via toPDF(). How you get to having that string is up to you. You could build it in JavaScript, Apex, or a combination thereof.
    – sfdcfox
    Jan 15, 2021 at 15:47
  • and then this string will be rendered as pdf in the LWC html part ? Jan 15, 2021 at 15:56

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