I discovered this article via HackerNews and it really encapsulated my thinking about PDFs.
Extracts:
The format is intended and optimized for print. It’s inherently inaccessible, unpleasant to read, and cumbersome to navigate online.
Original – emphasis mine
Undoubtedly, PDFs were intended for print. If the web were designed by magazine layout experts using, oh, Quark Xpress (remember that?) or InDesign, sure, you could use a side-by-side two-column layout with giant pull quotes in different typefaces. In print, the dimensions of the page define the boundaries of your canvas.

Web browsers? Well, considering how differently browsers handle CSS layout, how users can change display size and font size, and most importantly of all users can resize browser windows at will, and all your static layout decisions fail.
Do not use PDFs to present digital content that could and should otherwise be a web page.
Used to be the only reason people did this was to force college students to retype rather than copy/paste to plagiarize.
Stuffed with fluff. PDFs tend to lack real substance, compared to regular web pages. When you’re building out a web page, you can visibly see how long it’s getting and how far users will have to scroll to consume the content. Methods of structuring and formatting digital content such as chunking, using bullets, subheadlines, anchor links, and accordions help users efficiently skim and scan sections that may contain the answers they seek amid long-form copy.
Amen. PDFs “tend to lack real substance” because PDFs use words as an adjunct to graphic design — like the old newspaper “column-inches” unit of measure.
Any PDF you’re considering digitizing? Do this as an exercise: print it out. Take a red pen (or an editor’s pencil if you’re lucky enough to have one) and read the damned thing with that pencil in your hand and strike through every vapid sentence, every prolix paragraph, every unnecessary adjective.
Then? Well, if there’s anything left, by all means, make it a mobile-responsive webpage.
Sized for paper, not screens. PDF layouts are often optimized for a printed sheet of paper, which never aligns with the size and scale of the user’s browser window. Regardless of whether they’re viewing the PDF on desktop or mobile, users can say “so long” to smooth scrolling and hello to tiny, unreadable fonts.
My particular pet peeve with this point: when I’m reading a two-column PDF and I have to choose between leaning forward and squinting at one whole page on the screen, or resizing the window so I can easily read it and then scrolling up to the top of the page to continue reading in column 2. I nearly always wind up on a totally different page.
On mobile? Hilarious. Even worse? I still use a gen 3 Kindle to read ebooks. When I open a PDF on my Kindle, I’m presented with print so small the e-ink display struggles to render it.
Navigation — I frequently see this issue with PDFs. I click somewhere on the document, then use my mouse wheel to scroll further along. At some point, I use the down arrow key or page down or click the Next Page button — only to discover the PDF cached my current-reading-point based on the initial mouse click. So instead of getting the next page in what I’m reading, I get the initial-click+1 page. And then I’m grumpy.
There’s this old joke about SEO: What’s the best place to hide a dead body? Page 2 of Google search results. (Har har.) I’ve realized page 2 of Google is in fact the second best place to hide a dead body…