Not OP. Xiaomi MIUI bundles WPS office, which has a "mobile view" for PDFs. It's far from perfect, but it can single-column some multi-column PDFs. Some PDFs, like restaurant PDFs are downright butchered though.
According to the article Adobe reader for Android got this feature recently. I tried it and I am disappointed. Maybe OP was talking about reflow mode that indeed was accessible in many pdf readers, but for technical papers (math) it was useless.