We do not handle encrypted PDFs at this time. However, 3rd party tools are available to remove encryption from documents before importing them into Semantik. Here at Ephesoft, we use Foxit PDF Reader, which you can download and use for free from here.
Once you have installed Foxit, follow these instructions:
Open the invoice in Foxit
Select "Print to PDF" (to e.g. your desktop)
Import the invoice that was saved to your desktop into Semantik