I recently had a remarkable teaching experience.
I was teaching on typographic accommodations that support visual readers with low vision. I had explained how there are more than 20 common ways to get low vision and these can attack about 15 systems in the eye and brain. This means that low vision does not manifest in a uniform way. That is one among many reasons why individual choice of typographic setting is so important for visual readers with low vision.
I had gotten to the point where I show style sheets that had worked for real people in my experience. I told the anecdote about my friend, Bob, who looked at my favorite style and said, "If I had to look at that all day, I'd puke". When I put up a style a woman in the middle row got very uncomfortable. She said, "Could you turn that off? It makes me ill to look at it, or I'll have to leave the room". I quickly changed the style sheet, and she went on to say that she finally understood what was wrong in her life. People kept shoving solutions to her visual problem at her, and they told her she was crazy for claiming that they didn't work. She said, "When people call you crazy long enough, you begin to believe it".
I spent the rest of the day finding a style that would please her. With, ZoneClipper, experimental software developed by Abhay Mhatre and me, she now reads the HTML articles she needs for her work in comfort.
Had PDF been the medium, there would be no happy ending. My student and I are both grateful for the gift of style choice we get from HTML+CSS, but PDF obstructs choice.
Don't Blame Yourself
If you have low vision, and you have lots of trouble reading PDF files, you are not alone, and you are not doing anything wrong. Chances are, there is no way you can make that PDF document look like you need it to look. The reflow option on the Adobe Reader is buggy. Saving as HTML usually introduces many errors even with properly tagged PDF. The widely touted claim of PDF accessibility excludes you. My advise to my community of visual readers with low vision is do not blame yourself, just dig in and treat your PDF document like it is paper. For you and me PDF is effectively paper.
Contrast PDF With HTML
PDF does not separate content from presentation, at the level needed to support reading with low vision. PDF allows the ability to distinguish between headings, paragraphs and lists elements even if you cannot see the text. It enables document element navigation like heading navigation. This is one level of separating of content from presentation, but it is incomplete.
Most other technologies allow element level detection, but they also support separation of presentation from content, all the way down to the individual letter of text. This is the level people with low vision need. The visual style preferences of people with full sight shut readers with low vision out of reading most text. Font sizes, visually confusing font faces, kerning, single spaced lines and disorienting color schemes like the standard black print on white background are just a few factors of presentation that contribute to impaired perception of text. PDF cannot remove most of these barriers. It can adjust size and color in limited ways, but that is it. Within a PDF file, the style and content of text are inextricably tangled.
When you contrast PDF with HTML, you understand just how limited the visual choices are for PDF. HTML and CSS enable every change in text presentation needed to include low vision. With HTML and CSS you can choose font family, font size, color, spacing (line, word and letter), margin size and borders. Moreover, you can apply different presentations to different document elements. Headings can have one look. Paragraphs can have another look that visually distinguishes them from headings. Lists can have another look. Visual readers with low vision need visual cues to separate the semantic elements of documents. They are like people with full sight, they just need different visual cues.
The templates for most word processors supply a similar range of changes in presentations. They are not as clean as HTML with CSS, but they work. PDF is unique in its extreme inflexibility. That is why it is inaccessible for visual readers with low vision. It denies the freedom necessary to adjust the presentation of text. People with low vision just cannot get the flexible typography they need to read, especially professional materials. PDF files, even tagged PDF files, just cannot deliver.
I never read PDF for fun. It usually causes me physical pain and nausea. I make numerous reading errors. Of my many friends with low vision I know none who can finish long documents in PDF using Adobe Reader. I have finished two in my lifetime.
Most of the time, I print the document. I use Xerox enlargement to get a 140% bump in size. Then I use a 2.5x hand magnifier. That gives me 350% enlargement, sore eyes and a very stiff neck. PDF is just too much for my reading stamina.