PDF articles are notorious usability disasters, with the worst being multi-column documents that require you to constantly scroll in opposite directions as you move through the columns. PDF readers should let us draw a simple path through the document (maybe zoomed out) to outline the flow of text through the article (better, it could try to guess this for us). Once the path is set, the PDF reader could either:
A) tie the scrollwheel linearly to the text flow, so that simply scrolling down shifted the document to the next column to read. Maybe grey-out the columns not actively being read.
or B) rearrange the columns to make the document single-column.
Reading PDFs shouldn’t be so painful.
I should mention regular multi-column web pages have the same issues on mobile browsers. There’s a good case for using media queries to switch small viewport devices to see single-column layouts, and generally keeping all long articles single-column.