How to convert two columns of text in a pdf into one column in a new file?
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.