How to increase the scale of PDF maps?

I've just started using this website for routemapping, which is super helpful.

When I download PDF 'touring scale' maps, the maps themselves are approx 70% of the page size, so when I print them at A4, they're small and not very legible. Ideally, I'd like the maps to fill all/most of the page. I tried to copy and paste them into a Word doc to edit, but the images don't come out. 

Does anyone have a workaround please? Thanks! e.g. https://cycle.travel/map/journey/629315