Hi, @Jackie79 !
Thanks for reaching out to us. This project sounds incredibly interesting. I'd say the most universally used file type for this type of thing is EPUB, or electronic publication. This is an eBook format and can be read on a variety of devices, including computers, smartphones, tablets, and most eReaders. I'd recommend using EPUD in coordination with the Digital Download's Shopify application to create these digital products in your store. This app will provide your customers with the download file for their purchase.
Let me know if you have any further questions!
Hi Jackie! Walter from microDev here (Shopify Partner).
This is a wonderful idea and we would love to help you make it a reality. For flipbooks, the format used is generally HMTL5 to display in a browser (like a brochure format), but you would need to pay for a PDF to HTML5 converter or use a free one that has ads and a watermark (not professional though). PDF will be the most universal format if you want to share it with as many people as possible across all platforms. Another solution could be to publish it as an ePub, but you would need to install an eBook reader app on your computer or tablet then.
With regard to "Pay what you want" button, there are ways of doing this, but you cannot simply adjust the price as this could be used to scam clients. The easiest and best way I could think of is to create variants with different prices that they could pick from at a regular interval, say $1, $2, $3, $4, etc.
If you want any help implementing any of this or building/customizing this website, please feel free to contact me at support@microDev.today and we can see how we can help you with this worthy cause!