If you get an error that looks something like this when trying to create a PDF Invoice or Packing Slip:
Fatal error: Call to undefined method DOMText::getAttribute() in /home/yoursite/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/lib/dompdf/include/cellmap.cls.php on line 437
This means that there is an error in the HTML source of your template. Mostly, this is caused by plugin output or errors in the middle of a table, where it shouldn’t output anything at all.
For example, the HTML could look something like this:
<table> Umsatzsteuerbefreit nach §4 UstG <tr> <td>Label</td> <td>€10</td> </tr> </table>
This particular example was caused by a wrong use of a WooCommerce action to display a text, but it wasn’t printed correctly as table data (more information here).
To determine the cause for your particular error, you can (temporarily) output the invoice data to HTML, by turning on the ‘Output to HTML’ setting in the Status tab of the PDF Invoice settings.
Next, create a PDF invoice from the WooCommerce backend. You can now view the HTML source of the document to see if you can find anything wrong with the HTML. If you don’t see anything or don’t know what to look for, you can also try running the template output through an HTML validator (like http://validator.w3.org/#validate_by_input).