Must install wkhtmltopdf, this module is missing a README.md file and also missing a help hook

When I click on the "Download as PDF" button I get this message:
Sorry, we were unable to download retrieve the PDF at this time. Please try again later.

Im also seeing the same, the required library pulled down via Composer.

Seems to fall over at $pdf->toString(), im yet to determine why.

Until this issue is resolved:
✨ add support for the dompdf library Active

You'll need to install the wkhtmltopdf library on your server.

Here's the instructions:

→

https://wkhtmltopdf.org

@TODO, add a README and help page for book_pdf.