Help on the site, with wordpress?

Question

Web development

Hello!
There is a site on WordPress
There is a plugin, PDF viewer v 0.1
Opens PDF files in its own window in a new tab, everything is fine!
PDFs are books.
There is one huge minus you can not tap resolution with your fingers.
Advise the plugin or how to solve this problem who faced.
Or maybe use books not in PDF but in another format, then with what extension.