Signature in the bottom of the invoice

Hello @aditya2525

In fact with our Premium Templates extension is more simple, you just need to add the image to a custom block, like below:

Alternatively you can add the code snippet below to your theme functions.php file:

add_action( 'wpo_wcpdf_after_document', 'wpo_wcpdf_add_custom_signature', 10, 2 );
function wpo_wcpdf_add_custom_signature( $document_type, $order )
{
	if( !empty($order) && $document_type == 'invoice' ) {
		echo '<img src="https://wpovernight.com/signature.jpg" style="height: 5mm;">'; // replace with your image url
	}
}

You could style is adding custom CSS to the style property.

If you never worked with actions/filters, please read this documentation page: How to use filters