Digital Edition :Unable to search keywords in search bar

I use digital edition of a textbook (if it matters, it's Human Life Its Philosophy and Laws: An Exposition of the Principles and Practices of Orthopathy by Herbert M. Shelton) and it opens perfectly well in the Adobe Digital Editions software (I'm onMac OS X Version 10.11.6 (Build 15G22010)and although I can type a search term in the search field, nothing happens.

Any suggestions? The reason I bought a digital edition was to be able to search, so this has been a problem.

Thanks!