Reading a PDF comfortably on a tablet or phone

PDFs are supposed to be miserable on a tablet. Mostly they are, and mostly it is for one reason that takes ten seconds to fix at conversion time and is impossible to fix afterwards.

The mistake

Almost every PDF you have ever opened on a tablet was made for a sheet of A4 paper. Your tablet is not a sheet of A4 paper. It is smaller, a different shape, and held much closer to your face.

A PDF reader has exactly one move available: scale the whole page to fit the screen. So an A4 page designed for 90 characters across, read at arm’s length on paper, gets shrunk onto a 10-inch display, and the type arrives at a size nobody would choose. You zoom in. Now you can read it, but the page is wider than the screen, so you pan left and right on every single line. That is the experience people mean when they say PDFs are bad on tablets.

The fix, which is counter-intuitive

Make the page smaller. Do not make the type bigger.

This surprises people, so here is the arithmetic. Suppose a 10-inch screen:

Setting	Characters per line	Effective size on screen
11pt on A4	~90	tiny
14pt on A4	~70	slightly less tiny
11pt on a tablet-shaped page	~55	comfortable
11pt on a phone-shaped page	~35	large

Increasing the type size makes the page hold fewer words, but the page is still scaled to the same screen, so you gain very little and add a third to the page count. Shrinking the page holds fewer words and gets magnified more when it is fitted to the screen. The page size is the real zoom control.

The practical version:

• Tablet — page size “Tablet screen (4:3)”, 11pt, narrow margins.
• Phone — page size “Phone screen (16:9)”, 12pt, narrow margins.
• Something that also prints — A5, 11pt. A compromise, but a far better one on screen than A4.

Narrow margins because screen margins are wasted: nobody holds a tablet by the paper. The same arithmetic, framed around line length rather than screens, is in choosing a page size and margins.

Turn justification off while you’re there. A tablet-shaped page gives you a narrower column than A4, this converter doesn’t hyphenate, and justified text at that measure has to stretch its word spaces far enough that you can see the gaps. Ragged-right reads better on any small page.

Turn page furniture off too, for the same reason margins go narrow. A running head and a page number cost you two lines out of maybe thirty. On paper that’s a rounding error. On a phone-shaped page it’s seven per cent of the screen, spent telling you the title of the book you’re holding.

Scrolling mode is the other half of the fix

Almost every reader has a setting that switches from page-at-a-time to continuous vertical scrolling. On a phone it transforms the experience, because a phone-shaped page plus continuous scroll behaves almost exactly like a reflowing ebook: you swipe up and the text keeps coming.

• Apple Books — tap the top of the screen, turn on Vertical Scrolling.
• PDF Expert, Xodo, Documents — a view or scrolling option in the toolbar.
• Adobe Acrobat — the continuous scrolling toggle in view settings.
• Firefox and Chrome — scrolling by default.

Page-at-a-time suits a tablet held in landscape. Continuous suits a phone. It costs nothing to try both.

Turn the bookmarks on

On paper you find a chapter by riffling. On a screen there is no riffling, so the PDF outline, the sidebar list of chapters, is how you move around a long document. It costs nothing and every serious reader shows it:

• Apple Books — tap the contents icon, top left.
• PDF Expert, Xodo, Documents — a bookmarks or outline panel.
• Adobe Acrobat — the bookmarks tab down the side.
• Google Drive’s viewer — the contents button.

The generated contents page is worth having too, because its entries are tappable links that jump straight to the chapter. Between the outline and the contents page, one of the two is reachable in whatever app the file ends up in, which is the reason both are on by default. EPUB to PDF with page numbers explains what each of the four bits of navigation furniture is actually for.

One thing to know before you go looking: on a phone the outline is usually two taps into a menu rather than a visible sidebar, and in macOS Preview it stays hidden until you pick View, Table of Contents. Plenty of people conclude a PDF has no bookmarks when it has a perfectly good set.

Reading on an e-ink device

A Kobo, a Kindle or a reMarkable is a different problem again, and mostly a harder one.

The screens are small and can’t be zoomed smoothly, refresh is slow enough that panning is painful, and none of them reflow a PDF. So the page size has to be right at conversion time, because there’s no recovering afterwards.

Rough guidance: for a 6-inch reader, use the phone-shaped page, 11pt, narrow margins, justification off, page furniture off. For a 10-inch device, A5 works well. Convert one chapter and put it on the device before you convert the whole book, because e-ink punishes a wrong guess more than any other screen.

And if the device opens EPUBs, which every Kobo and Kindle does, think hard about whether you want a PDF at all. See below.

Getting the file onto the device

However you normally move files. AirDrop to an iPad offers to open it in Books. On Android, drop it in Drive or the device’s own storage and open it with whatever reader you like.

There is no service in the middle here. The PDF was built in your browser and it is sitting in your downloads folder. Nothing was uploaded, so there is nothing to sync and no account to make.

When you should not do any of this

If you just want to read the book, and your device opens EPUBs, read the EPUB.

That is the honest advice. An EPUB reflows to your screen, your font and your chosen type size, adapts when you rotate the device, and remembers where you were. No PDF can match that, because a PDF’s pages are fixed by definition, which is the entire reason it is useful for everything else.

Convert to PDF when you need something only a PDF gives you:

• Fixed page numbers, to cite or to discuss with someone reading the same file.
• Annotation in an app that takes nothing else, which is most of them.
• Handing it to someone whose device will not open an EPUB.
• Printing, obviously.
• Archiving, where a format that will still open unchanged in twenty years is worth more than one that reflows.

That list is short on purpose. If none of it applies to you, read the EPUB and don’t convert anything.

The quick version

• Page size is the zoom control. Type size barely moves it.
• Tablet-shaped page for a tablet, phone-shaped for a phone, A5 if it has to do both.
• Narrow margins, justification off, page furniture off.
• Turn on continuous scrolling in whatever you read in.
• Find the outline before deciding it doesn’t have one.
• If you just want to read the book and the device takes EPUBs, read the EPUB.