Hi Andrew,
Thanks so much for reaching out and thanks for using Crio Pro WordPress theme!
I would definitely try converting your PDFs on a third party software before uploading to WordPress. WordPress conversion is not the best and you’ll always lose some resolution. The best option is to use a PDF convertor tool and couple that with a free image editing software like Pixlr.
I hope this helps. Please let us know if you have any other questions for us.