Invoice and quote PDF files use a customizable template file system in the templates directory of the active WHMCS system theme.
The General tab in General Settings allows you to configure basic settings within WHMCS, like the company name, your logo, system URL and theme, maintenance mode, friendly URLs, and more.
How to troubleshoot TCPDF image size errors while downloading invoices.
How to troubleshoot TCPDF timeouts during invoice generation.
You can customize the styling for emails that WHMCS sends to your customers by configuring custom global email headers and footers.
You can easily change the logo in emails, on generated invoices, and in the Client Area.