Crop the margins of a scanned PDF
Draw one crop over the pages stacked on top of each other, and it trims the white margins, the scanner edge and the spine shadow from every page of the book.
Key takeaways
- On an e-reader, every millimetre of margin shrinks the text, because the whole page is scaled to fit the screen.
- Cropping to the printed area can make the text noticeably larger: about 29% in the worked example below.
- Most PDF tools crop by a box you drag on one page. A scanned book moves about on the glass, so one box rarely fits page 300.
- FixMyScan stacks 50 pages on top of each other so you can see where the text sits across the book, then applies your one crop to every page.
- Crop past the spine shadow and the scanner's dark edge, but leave the page numbers in if you cite them.
Why margins matter more on a screen than on paper
On paper, a margin is somewhere to put your thumb. On an e-reader, it costs you text size. A PDF keeps its page shape, so the reader shrinks the whole page, margins and all, until it fits the screen. Whatever space the margins take is space the words don’t get.
A scanned book usually has more to trim than the printed margin:
- the white border the printer left round the text
- extra paper round the page, because the scan caught more than the page
- the scanner’s dark edge or the lid’s shadow
- the grey shadow where the page curves into the spine
A worked example
Take a book printed on a 6 × 9 inch page, with the text block 4.4 inches wide and 7 inches tall. Say your screen is 3 units wide for every 4 units tall.
- Uncropped: the page is taller in proportion than the screen, so its 9-inch height fills the screen height. The 7-inch text block fills 7 ÷ 9, about 78% of the screen height.
- Cropped to the text block: the block is now the page. At 4.4 × 7 it is still taller in proportion than the screen, so its 7 inches fill the full height.
The text goes from 78% to 100% of the screen height, which is 9 ÷ 7, about 1.29 times bigger. On a scan that also caught a dark border and some desk round the page, the gain is larger. Your own numbers depend on the book and the screen, but the arithmetic always runs the same way.
Why one box rarely fits a scanned book
The crop tools in most PDF editors assume every page sits in the same place:
| Tool | How it crops | Whole book |
|---|---|---|
| FixMyScan | One box drawn over 50 stacked pages | Every page, up to 1,000 |
| iLovePDF | Drag a box on one page | All pages or the current page |
| Smallpdf | Drag a box on one page | Single page or all pages |
| PDF24 | Set margins or draw on the page | No auto-detect mentioned |
| Sejda | Auto-crop, or the same crop for all pages | Within its page limits |
| ScanTailor Advanced | Content selection and auto margins | Yes, Windows and Linux desktop |
The trouble with a box drawn on one page is that a scanned book drifts. The book moves on the scanner glass. Left pages and right pages have the gutter on opposite sides. A phone scan is a little closer on one page than the next. Draw the box on page 10 and it may clip a line on page 240.
FixMyScan shows 50 pages from across the book laid over each other, so the printed area of the whole book shows up as one darker block, and pages that sit off-centre are visible at once. Draw the box round that block and nothing gets clipped.
How to crop a scanned book
- Upload the book. A scanned PDF or DjVu file, up to 1,000 pages.
- Look at the stacked pages. Find the page numbers, running heads and footnotes, and decide which you want to keep.
- Draw one box. Keep it just outside the printed area, past the spine shadow.
- Let the rest run. The same pass straightens pages, whitens them and adds searchable text.
- Check flagged pages. Any page whose content falls well outside the usual area is flagged for you to look at.
- Download and read. Send the PDF to your Kindle, Kobo or reMarkable.
How much to keep
Best suited for: reading on a 6 to 8-inch screen, where every bit of width counts.
- Keep page numbers if you cite the book or use its index. They are small and sit at the edge, so they cost little.
- Drop running heads (the book or chapter title repeated at the top) if you read for pleasure. They take a line on every page.
- Leave a sliver of white round the text. A crop right up against the letters looks cramped, and slight differences between pages can clip a descender.
When cropping isn’t enough
If the text is still small after cropping, the type itself may be tiny, or the book may be large-format with two columns. PDF text too small goes through the other options, from landscape mode to a bigger screen.
Questions
How do I crop multiple pages in a PDF at once?
Most editors have an 'all pages' option for a crop box. iLovePDF and Smallpdf both let you drag a box and apply it to every page. That works when every page is in the same place, which is true of a typed document and seldom true of a scan.
Why can't I just use auto-crop?
Auto-crop trims each page to its own content, so a short last page of a chapter gets blown up and a full page doesn't. The text size jumps as you turn pages. A single crop for the book keeps every page at the same scale.
Will cropping cut off page numbers or footnotes?
Only if your box excludes them. The stacked view shows the page numbers and footnotes of 50 pages at once, so you can see where they sit before you set the box.
Can I remove the black border from a scanned PDF?
Yes. The dark edge from the scanner lid or bed sits outside the printed area, so the same crop removes it.
Does cropping reduce the file size?
A little, because less image is kept. The bigger saving comes from turning grey pages into clean black and white, which happens in the same pass.
Can I skip the crop?
Yes. You can set the crop step to skip in your settings, and the book is cleaned and made searchable at its full page size.
Does it change my page numbers?
No. Pages keep their order and number. Only the white space round them goes.