Sumatra PDF might be a bit more popular than Piio. We know about 1 link to it since March 2021 and only 1 link to Piio. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
Piio.co — Responsive image optimization and delivery for every website. Free plan for developers and personal websites. Includes free CDN, WebP and Lazy Loading out of the box. - Source: dev.to / almost 3 years ago
You can use your browser for both, there are extensions(FireFox - PDF & EPUB/Chrome - PDF& EPUB) for that. In case, you want you use a separate software for them, I suggest SumatraPDF--it handles both PDFs and .EPUB files. Source: over 1 year ago
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