Research spanning 20 years proves PDFs are problematic for online reading. Yet they’re still prevalent and users continue to get lost in them. They’re unpleasant to read and navigate and remain unfit for digital-content display.
R. Stiefelhagen, and J. Yang. Acoustics, Speech, and Signal Processing, 1997. ICASSP-97., 1997 IEEE International Conference on, 4, page 2617-2620 vol.4. (April 1997)