Hi Nina,
While there is no build-in tool in KNIME to extract images from PDF files, you can use the pdfimages tool to do so. I attached a workflow that demonstrates this. The pdf you submitted actually contains a series of pictures which need to be combined into one, which is what I am also doing in there with KNIME nodes.
On linux, pdfimages is a part of poppler. On windows you need to install XPDF. In any case I hope this helps you with your question.
best,
Gabriel