Good Morning sir, Boss, In Quickbooks When i am going to invoice print preview its good. But in sales print its not working . Massage Error Failed to load PDF document.

Welcome to the Community, @mdr03514. 
 

Let's troubleshoot your web browser to determine what's preventing you from printing sales forms using QuickBooks Online (QBO).

Here's how:

1. Relaunch your web browser.
2. Open your QBO account using a private window.
3. Delete your browser's cache.
4. Include Intuit as a trusted site.
    

I'm also adding this article for reference on how to customise sales forms in QBO: Customise invoices, estimates, and sales receipts in QuickBooks Online.

If you have further questions about printing sales forms or any other concerns inside the program, please let us know. We're always here to help. Have a good one.