<apex:page showheader="false"
contentType="text/html;charset=UTF-8"
renderAS="PDF"
sidebar="false"
standardStylesheets="false"
applyHtmlTag="false"
applyBodyTag="false"
readonly="true"
cache="true"
controller="ReportFormController"
>
renderAS="PDF" 설정을 꼭 해줘야 한다