How to read PDFs on the Kindle (or smartphone, or any small-screen device) – revisited


Kindle PDF2Converting PDFs to the Amazon Kindle is not a straightforward affair. While there are many tools that can do the conversion to another format such as .MOBI, re-casting a typical PDF document into an ebook that works on a small screen requires more than mere change of format.

Formatting a PDF for the kindle can be done in two ways; the first is to CROP a PDF ebook then change it into a Kindle friendly file format. This allows for continuous text, uninterrupted with headers, footers, and page numbers, that is very much Kindle-friendly. You can read a detailed tutorial about this by following this link (henceforth referred to as ‘my first post’).

The second way is to essentially do the same thing as described above, but in an automated way that takes all the manual intervention and decisions out of it, using a free program called K2PDFOpt. This software works by converting your PDF to bitmap images, identifying the viewable areas, then assembling these into smaller pages without excess margins. Not only does this automate the work, but is ideal for multiple column documents. It has both advantages and disadvantages as detailed below.

How to convert with K2PDFOpt

1. Download K2PDFOpt (free software available for Windows, Linux, and MacOSX).

2. Grab the PDF document (or multiple documents, or a folder full of PDFs) and drag them to the K2PDFOpt icon. K2PDFOpt will start processing and you will see a screen similar to the screenshot on the right;

3. Once finished, new PDF files will be created in the same location as the originals with _k2opt at the end of the name of each.

The kind of results to expect:

1. File size: each resulting PDF will be much larger in size than the original (a 2 meg PDF was transformed into a 58 meg file).

This is because K2PDFOpt actually transforms the ebook into image bitmaps first before repackaging it as a PDF.

2. What the PDF will look like: see below for some examples

Pre K2PDFOpt Screenshot
Before processing
Post K2PDFOpt Screenshot
After processing (showing 2 pages)

See also results for 2column (from the program web site)

2 Col Pre K2PDFOpt Screenshot
Before processing
2 Col Post K2PDFOpt Screenshot
After processing (showing 2 pages)

However, there were instances where the pages had random text artifacts that were incorrectly sized (see screenshot below)


The text in large font on this page in fact was not supposed to be sized differently from the rest of the text.

PROS: the advantages of using K2PDFOpt (vs. doing it manually as per my first posting)

1. Fully automated. No work on your part is necessary, no decisions to be made

2. Can process books in batch: which is helpful if you have a folder choc full of PDF ebooks that you want to process en masse. Note, though, that this can take a very long time, so you might want to do it overnight or something like that. Also watch out for file sizes, which can get out of hand (see below).

3. Works very well: generally speaking

4. Works well for documents containing columns: which are even more labor intensive if cropped/process as per the first post.

CONS: the disadvantages of using K2PDFOpt (vs. doing it manually as per my first posting)

1. You can potentially get better looking documents: if you you crop manually then convert. In some cases, cropping alone can produce a Kindle friendly PDF.

2. File sizes: are very large when processed with K2PDFOpt. If you have, say 500 megs of PDF ebooks, you’re looking at something like 15 gigs of PDF files when K2PDFOpt has processed it. In contrast, file sizes will not increase with the cropping/conversion operation described in the first post. (You also have to think about the hard drive size of your Kindle if you’re going to be adding many big files to it).

3. Headers/footers still find their way into the document: which is to say, you don’t really get an uninterrupted text flow, as you would from a native MOBI ebook for example.

4. Converting text to images reduces functionality: for example it makes the document unsearchable, un-highlightable; words cannot be translated, etc.

The verdict: K2PDFOpt is a brilliant and remarkably effective tool. I am amazed just thinking about the planning that had to have gone into figuring out the logic and execution of this beautiful piece of software.

Having said that, I still think there is a place for cropping and converting PDFs manually as described in my first post, just because there is at least the possibility of an even better outcome.

But in terms of convenience and ease of use, K2PDFOpt is king. It is the closest to a 1-click solution for PDF to Kindle conversion that you can get.

[Thanks go to reader Willus for tipping me off about K2PDFOpt in the comments section of my first post on this subject]

  • Lee

    Another, much easier and better way is using the Mobipocket Creator. Instructions can be found on this Web site:

    It converts it to the *.prc version for the Kindle, making it work just like a regular Kindle book, e.g., you can adjust the text size, make bookmarks and notes. I have used it on many different PDFs and it really works great! There are a few problems with large images but I have only found these problems to be with the cover.

  • Another disadvatage I can see is that by converting the ebook to images you loose out on being able to select works and see there dictionary meaning. Correct me if this is wrong.

    Alternative solutions that are a bit radical is using 3rd party firmware on your kindle. Duokan does automatic margin cropping when reading pdfs.

  • rjh

    This might work OK for very occasional use, but I don’t see why PDF in any size is desirable to reading on screen.

    Calibre does a very good job of converting PDF text documents into suitable ebook formats. Includes tools for cleaning up headers, footers, page numbers etc – and also free.

  • willus

    I realize there are PDF-to-ebooks creators out there, but one of the reasons I wrote k2pdfopt is that I was very disappointed with most of the results when converting 2-column tech articles. Typically the graphics and equations did not come through the conversion process well with the PDF-to-ebook conversion tools, but maybe they’ve gotten better.

    • Samer

      @ willus: thanks for an amazing program. The concept behind K2PDFOpt is pure genius!

      As far as I am concerned, a definite must have for anyone who has a Kindle and PDF documents that were never designed for a 6″ screen.

  • willus

    For anyone who downloaded v1.11 (or older) of k2pdfopt, you should get the latest version, v1.12 (I uploaded it on July 20). It fixes a bug that caused pages after page 7 to not be shown in Adobe’s reader. Samer–thanks. Very kind of you.

  • willus, thank you for great k2pdfopt. 🙂

    Can you make some options in programm?

    1. As I can see, Kindle has 600×800 resolution, but my ebook only 480×800. In this case text looks dirty.

    2. Can you make align on left side, not on cemter of the screen? 🙂

  • willus

    Vladimir–try the latest version (v1.13), posted 7-25-11. See the help page for how to configure custom settings.

  • Tried v1.13. But it doesn’t want to understand key “-w”.
    I just copied your example “-j 0 -w 480 -h 800” –

  • willus

    Vladimir — Whoops! Sorry. Try v1.14.

  • Great!
    In 1.14 “-w” works perfectly.

    Can you give some link where I can read more about idpi and odpi?

    I tried “-j 0 -idpi 300 -w 460 -h 768 -odpi 96″ for my 7” 800×480 e-book and it looks not bad, but it’ll be easier to get good result, if I understand how dpi works. 🙂

    -w 460 – because I want a bit margin from left side.
    -h 768 – because there is some info line with battery status and so on.

    But the result is a bit strange.
    Original book:
    “-j 0 -idpi 300 -w 460 -h 768 -odpi 96”: – why such a large margin on the right?

  • willus


    -idpi sets the resolution of the source bitmap but does not affect the magnification or size of the output. Just the fidelity. Set this higher to get better looking output. Typically you want it to be at least as high as -odpi. Try setting it to a low value just to see what I mean.

    -odpi sets the dpi of your destination screen, so if you use -odpi 96 on a 460-pixel wide screen, you are telling k2pdfopt that you want it to show 460/96 = 4.8 inches of text width from the original document on your display. That’s probably too much. Let’s say you have a 2-column document where the columns are 3.5 inches wide. Then you should set -odpi = 130 so that 460/130 = 3.54 inches and a single column will fit nicely on your reader. If you set -odpi too much larger than 130, then k2pdfopt will wrap the lines of text (try it). If you set it too much smaller, you’ll have a lot of margin on the right, which is probably what happened in your case (I can’t access the links right now, so I don’t know).

    I don’t have a way to set the left margin at the moment. It would not be hard to add another option for that.

    Maybe send me an e-mail (“about the author” on my web site) so we don’t have to keep discussing this on this forum.

  • My personal choice : Adobe Reader App. i bought an iPad this year, before the Adobe reader app released, reading PDFs on iPad is really a pain. i used to convert it to epub in order to read it properly on my iPad.

  • zaneef

    Everyone says this software is easy to use. Unfortunately, i havent noticed that. Dragged and dropped the documents and i kept getting prompts.

  • CARLD55

    you should try BRISS it automatically crops a pdf margins, its free and it does the work in ten seconds

  • Uchiha Itachi

    This make me think about the UI PDF Viewer control. Bravo!

  • Ebook Lover

    I have a pdf which is an academic/ technical book.

    The book has lots of tables and diagrams

    Hats off to willus.. k2pdfopt did it without losing a single diagram.

    I could not find any other option (I tried so many including mobipocket) that could preserve the tables and diagrams in the book..

    Even the greatest of the apps have their own limitations and this has too.. The major one being not being able to highlight or take notes and not removing header and footers which are added as additional pages/ text in the resulting book

    But the been said, if you are reading anything that is remotely close to technical/academic book I think it would be immensely difficult for you to find an app better than this..Thanks Willus.. Great work again

  • Karan Asthana

    How to convert K2pdfopt to EPUB or MOBI,I hate the transition while opening a PDF in Kindle