How to convert two columns of text in a pdf into one column in a new file? So that I can listen to it with a phone app, I am trying to copy a textbook with two columns of text into a file with one column. Selecting all and pasting results in the right-hand column of each page appearing before the left, so that half of each page is out of order (the reader app perceives the text the same way, and reads each page right-column-first). 

I would be very grateful for insight. How can I create a file with correctly ordered text?
There is an app named k2pdfopt that, according to the website: "K2pdfopt optimizes PDF/DJVU files for mobile e-readers (e.g. the Kindle) and smartphones. It works well on multi-column PDF/DJVU files ".  This app supposedly converts 2-column PDFs into 1 column. I haven't used it so I can't vouch for it. The app is free though so it should be worth a try.