In order to display Salesforce Visualforce rendered as PDF in a Flow, use iFrame tag in the Lightning Web Component and add the LWC in Flow Screen Element.

Sample Visualforce Page:

<apex:page renderAs="advanced_pdf">
    Testing PDF Conent in Flow
</apex:page>

Sample Lightning Web Component:

HTML:

<template>
    <iframe
        src="/apex/FlowPDFPage"
        height="100%"
        width="100%">
    </iframe>
</template>

JavaScript:

import { LightningElement } from 'lwc';

export default class FlowLightningWebComponent extends LightningElement {}

JS-meta.xml:

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>56.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__FlowScreen</target>
    </targets>
</LightningComponentBundle>

Output: