Proof of concept inspired by Matthew Hauck's question on the Success Community how to export Enhanced Note to PDF, https://success.salesforce.com/0D53A000035M8cM

ContentNotePDFController.java

/**
 * Developed by Doug Ayers (douglascayers.com)
 * 
 * Proof of concept inspired by Matthew Hauck's question
 * on the Success Community how to export Enhanced Note to PDF
 * https://success.salesforce.com/0D53A000035M8cM
 */
public with sharing class ContentNotePDFController {

    public transient String title { get; set; }
    public transient String content { get; set; }

    public ContentNotePDFController( ApexPages.StandardController stdController ) {
        ContentNote note = [ SELECT id, title, content FROM ContentNote WHERE id = :stdController.getId() ];
        this.title = note.title;
        this.content = note.content.toString();
    }

}

ContentNotePDFControllerTest.java

/**
 * Developed by Doug Ayers (douglascayers.com)
 * 
 * Proof of concept inspired by Matthew Hauck's question
 * on the Success Community how to export Enhanced Note to PDF
 * https://success.salesforce.com/0D53A000035M8cM
 */
@isTest
private class ContentNotePDFControllerTest {

    @isTest
    static void test_controller() {
        
        ContentNote cn = new ContentNote(
            title = 'Test Title',
            content = Blob.valueOf( 'Hello World' )
        );
        
        insert cn;
        
        Test.startTest();
        
        ContentNotePDFController controller = new ContentNotePDFController( new ApexPages.StandardController( cn ) );
        
        Test.stopTest();
        
        System.assertEquals( 'Test Title', controller.title );
        System.assertEquals( 'Hello World', controller.content );
        
    }
    
}

ContentNotePDFPage.html

<apex:page title="{!title}" standardController="ContentNote" extensions="ContentNotePDFController" renderAs="pdf" readOnly="true" cache="false">

    <h1>
        <apex:outputText value="{!title}"/>
    </h1>

    <apex:outputText value="{!content}" escape="false"/>

</apex:page>