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Crop PDF Margins for Reading on an E-reader
Updated
Short answer: Open Crop PDF, set the margins to trim in millimetres while watching the preview, and download a copy where the text fills more of the screen.
PDFs are laid out for paper, and paper needs margins. On a 6- or 7-inch e-reader, a full A4 or Letter page is shrunk to fit, so the generous white border costs you text size. Trimming it makes the words noticeably bigger with no zooming or panning.
Step by step
Step 1: Open Crop PDF and drop the file.
Open Crop PDF(runs on your device)Step 2: Set the top, bottom, left and right margins to trim, in millimetres. Start with about 15 mm each side for a typical document.
Step 3: Check the preview of the first page; keep a few millimetres of white so text doesn't touch the edge.
Step 4: Download the cropped PDF and copy it to your e-reader.
Step 5: If running headers or page numbers are still there and you don't need them, trim a little more top and bottom.
Why this works, and what to watch for
E-readers display a PDF page as a fixed layout scaled to fit the screen, unlike EPUB or Kindle books, whose text reflows. How much the page is shrunk depends on its visible area. If the margins take up a fifth of the width on each side, cropping them leaves three fifths, so the text can be drawn up to two thirds larger in the same screen width.
Crop PDF sets the visible area of every page to the margins you choose; the preview shows the first page with the crop drawn on it. The same crop applies to every page, which suits most documents. Scanned books are the exception: left and right pages often have different gutters, so a crop tuned for one side can clip the other. Choose margins that suit both, or split the PDF into the parts that need different crops and merge them afterwards.
Cropping hides, it doesn't delete. The trimmed area is still inside the file and can be recovered by anyone who resets the crop. That's fine for margins, but never use cropping to hide account numbers, names or anything sensitive: a cropped-out detail is still there.
Some practical numbers: a 6-inch e-ink screen is roughly 90 × 120 mm, about the size of an A6 page. A4 is 210 × 297 mm, so a full A4 page is shown at about 40% of its printed size. Cropping 20 mm from every side raises that to about 47%, and more if the document's margins are wider. For academic papers with two columns, cropping helps, but landscape orientation on the device often helps more.
Crop PDF runs in your browser, so your files aren't uploaded, and it's free with no limit.