@BetterRed: below is how the content of the epub looks like inside the ebook editor; it seems pretty standard text inside html paragraphs to me. Converting it using the print function of the viewer didn't solve the problem. I would like to use the acrobat reader android app on my tablet since it has very good annotation capabilities. Maybe it's not the pdf content itself but some metadata or descriptor that makes the reader think there is no text there. For every other document when I long press over a word it's selected but for the only two documents I produced with ebook-convert no word is selected and I get a menu with functions not directly related to text: note, highlight. Nevertheless text limits are somehow recognized since the highlight is done at character boundaries, it's not a generic rectangle tool. Also, other readers like evince in linux seem able to select text in both books. All this makes me think it's more a meta-thing than the contents themselves.
<p class="para" id="red0000630">The 75,000 pairs of genes that make and run the average human body find themselves in much the same position as 75,000 human beings inhabiting a small town. Just as human society is an uneasy coexistence of free enterprise and social co-operation, so is the activity of genes within a body. Without co-operation, the town would not be a community. Everybody would lie and cheat and steal his way to wealth at the expense of everybody else and all social activities – commerce, government, education, sport – would grind to a mistrustful halt. Without co-operation between the genes, the body they inhabit could not be used to transmit those genes to future generations because it would never get built.</p>
<p class="para" id="red0000631">A generation ago, most biologists would have found that paragraph baffling. Genes are not conscious and do not choose to co