To select text, you can 'tap-and-hold' on the text in the PDF and a context menu should pop-up with various options, including "Copy". Let me know if you tried that and it doesn't work for you.
It doesn't work with me, actually some of my short-text file just fine with copy-paste but the files in Japanese and long text nothing come out when I hold my finger on the screen. I need help!!
Europe, Middle East and Africa