How To Convert A PDF File For Better Kindle Or Smartphone Viewing

K2pdfopt is an easy to use PDF conversion program and produces PDF output files optimized for Kindle or smartphones. Yesterday I reviewed 2 easy methods to transfer a PDF file to a Kindle, using integrated USB transfer and Kindle conversion. Those methods may work fine for simple files, but more complex PDFs may look terrible on a Kindle…

The PDF standard was designed to always display documents in the same manner i.e. with a fixed layout, page size and text placement. This makes PDFs ideal for printing (as one page will always be printed on a single sheet of paper) which is why so many user manuals and brochures are in PDF format.

However, this fixed layout makes a complex, multiple column PDF file designed with large text/fonts (for easy viewing on a PC or laptop) extremely difficult to ‘shrink’ to fit a 6 inch Kindle display – and even harder for a smartphone’s tiny screen.

There are dozens of PDF conversion programs available to convert PDFs to a format more suited to a Kindle (or smartphone) but most work in a similar way – they basically ‘scan’ the PDF file into an editable format (like OCR, Optical Character Recognition) then shrink the page size, layout, text size etc and output back to PDF or another file format e.g. MOBI which Kindles can read natively.

Unfortunately this process is very hard to do well with complex PDF files. Even the developers of Calibre (one of the best conversion programs) state: “PDF is a really, really bad format to use as input. If you absolutely must use PDF, then be prepared for an output ranging anywhere from decent to unusable, depending on the input PDF”.

What is needed is a different approach such as that offered by the free K2pdfopt utility – the simplest and best PDF converter I have found for both e-readers and smartphones. Unlike most programs, K2pdfopt converts each page of the PDF to a bitmap, scans the bitmap for rectangular regions, then cuts and crops these regions before assembling them into multiple smaller pages – it doesn’t mess about with fonts and scaling like so many other programs do.

K2pdfopt Conversion Utility

  • K2pdfopt (Kindle 2 PDF Optimizer) is a free automated stand-alone (portable) conversion program
  • Any kind of PDF/DJVU file (best if it has a primarily white background) can be converted
  • K2pdfopt works especially well on two-column or multi-column PDF/DJVU files such as technical journal articles but even single-column files will often be significantly improved and much easier to read
  • It has the advantage over other PDF converters in that it fully preserves the rendered PDF fonts and graphics from the original file, unlike programs that convert the PDF to an e-book format
  • K2optpdf is independent of language or fonts so it will work equally well on documents in any language


How To Convert PDF Files With K2pdfopt

1. Download k2pdfopt from the developer here (Windows, Mac, Linux versions available) and save it to your desktop

2. Now just drag and drop your PDF file onto the k2pdfopt icon to open the program (accept any user control prompt to run it)

3. You will be met by a slightly daunting array of conversion options but don’t worry, you shouldn’t have to use most of them!

4. To optimize for Kindle (or other e-readers) skip straight to step 6

5. To optimize for Smartphones – type the letter o then press Enter. Type 250 then press Enter – this sets the default size for smartphones

6. Press Enter to use all the other default settings and start conversion

7. Depending on the size and type of PDF file (and speed of your computer) the conversion process may take a few minutes.

8. When finished, a new converted PDF file with _k2opt at the end of the filename is created in the same directory as the original file.

This converted file is optimized for viewing on Kindles and other mobile readers with 6-inch screens (if you left the options as default) or for viewing on Smartphones if you performed step 4. There are many other options in the interactive menu that you can use to tweak the settings and sizes etc further.

Tip: the developer has an excellent set of help pages here with illustrated pictures of each step in the process and more details on all the options – well worth a look.

Conversion Issues?

1. K2pdfopt converts color PDF files to mono by default (more suitable for e-readers) but you can choose to keep full color if you wish:

  • Before pressing Enter in step 6, type the letter c then press Enter. Now type Yes press Enter – this sets the color to full color instead of mono. Continue with step 6 by pressing Enter to start conversion.

2. The file size of the converted PDF file will be different to the original – in my test conversion of the free Windows 7 Guide e-book (previously featured here) the file size decreased from 24MB down to 11MB in default mono mode (22MB in color mode). However some PDF files may result in an increase in file size – it depends on the format of the original.

3. The number of pages increases dramatically e.g. in my Windows 7 book test above the total number of pages went up from 174 to 363 for the Kindle format. This obviously means that tables of contents and page number references to pages in the PDF will no longer be correct as there are more pages than before.

Post Conversion Processing?

If you have previously used Calibre to convert files you could run the output PDF converted by K2pdfopt through Calibre – as both programs work on different principles it is possible that Calibre could enhance the final output further to clean up the display of text. Calibre could also convert the PDF into another format such as MOBI etc if you prefer.


K2pdfopt is an excellent little PDF conversion program that is incredibly easy to use and produces PDF output files optimized for e-readers like Kindle or smartphones – and the fact that it is both portable and free is a welcome bonus.

The website help is superb too and includes detail of more advanced features e.g. you can drop a folder full of PDF/DJVU files onto the k2pdfopt icon to batch process them and can even drop a folder full of bitmap images to have them converted into a single PDF as if they were pages of a PDF file.

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3 Responses to: "How To Convert A PDF File For Better Kindle Or Smartphone Viewing"

  1. Shelley says:

    I tried this method, and found it worked a treat, except for one thing: because it turns the pdf into an image, the “highlight/annonation” features of the kindle don’t work. Rats. Back to the drawing board for me.

  2. Brian says:

    I tried to make a 350 page PDF (with images amongst text) work on my Kindle Touch and failed dismally probably because I am older and not particularly computer savvy.

    I finally came across the answer hidden at the very end of the website and it just works beautifully! See below…

    “If you prefer to have your personal PDF documents converted to the Kindle format so you can take advantage of Kindle functionality such as variable font size, annotation, Text-to-Speech, Whispersync, etc., type “convert” in the subject of the e-mail when you submit your personal document to your Send-to-Kindle e-mail address.”


    • Roy says:

      Hi Brian, ‘convert’ in the subject line is certainly the easiest way and if it works for your PDF that’s great, 350 page conversion is quite impressive :-)

      I covered ‘convert’ as one of the 2 ‘transfer’ methods linked to at the top but added this article because sometimes Kindle’s own converter doesn’t do a great job – it depends on the layout of the PDF.

      Certainly try the ‘convert’ route first – if you ever find it doesn’t produce a good format then k2pdfopt may be worth a try because it scans rather than converts, so keeps fonts/graphics intact