Find Missing Letters in Kindle PDFs

6 April 2018

I have a kindle paperwhite, but when I tried to read this pdf of von Neumann’s “The Computer and the Brain”, I found that some letters were completely missing.

Image of text on kindle with two missing letters
No-one could keep up with von Neumann's brain, but the mischievous Tipp-Ex demon wasn't helping.

On average a couple of letters per page were absent. It looked fine in other pdf viewers, so I knew the data was there. Following some suggestions online, I found that by far the best solution was ghostscript:

gs -o repaired.pdf -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress computerbrain.pdf

As for the other suggestions, Calibre and pdftocairo fixed nothing. And while mutool did work, I ended up with much larger borders which the kindle wasn’t able to trim. That means the text is much smaller than necessary.

By the way, it’s well worth reading.

Dear reader, good news

Missing letters and dodgy rendering is only ever a problem with scanned documents - computer-generated pdfs render without any problems. Here’s an example chosen entirely at random:

Random a4 pdf with equations
An example of a pdf built from LaTeX for A4, in landscape on a kindle paperwhite.