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An Introduction to E-Readers & File Formats

This is a beginner’s guide to e-readers and their file formats (primarily the differences between ePub and PDF).

It was written for people that are new to the concept of reading digital books on a digital e-reading device.

The difference between e-readers and e-ink tablets

The main difference between e-readers and e-ink tablets is that you cannot write notes on the screen of an e-reader. Essentially, e-ink tablets can do everything an e-reader can do but also support handwritten note-taking.

The E-Ink screen

All E-readers use a patented screen technology provided by E-Ink Corporation. Whilst there are different types of screen (e.g. Kaleido 3 (color), Carta (monochrome), Mobius Carta (flexible monochrome) etc.), all e-reader brands (Amazon Kindle, Kobo, Boox etc.) use screens sold by the same manufacturer.

E-Ink screens have several advantages that make reading more comfortable and eye-friendly than the screens on traditional tablets, smartphones, and computers. Firstly, they are not backlit, which means that they are not as bright. In addition, they have low refresh rates and draw a lot less power (which means the battery lasts far longer). I go into more detail about the advantages and disadvantages of e-ink screens in my Introduction to E-Ink tablets, but fundamentally, an e-ink screen is more pleasant to read on and closely resembles ink-on-paper.

So, whilst it is possible to read books on other types of screen (and plenty of people do, without issue), many people find the reading experience more comfortable on an e-ink screen and report less eye strain. If you are the sort of person that prefers to read physical books or regularly prints out documents to read, then an e-reader can provide you with the best of both analogue and digital experiences.

Advantages of reading e-books on an e-reader

As well as a paper-like reading experience, there are several other advantages to reading electronic books on an e-reader, including:

  • Quick dictionary definitions if you do not know what a word means
  • Ability to highlight passages of text and add sticky notes
  • Easily change the font-size, font-type and layout
  • Receive books instantly, rather than waiting for them to be shipped
  • E-books are often (but not always) less expensive than their physical counterparts
  • Search the text
  • All your books (your library) are easily accessible and in one place

E-Book formats (PDF vs ePub)

E-readers can open several file formats (including Word documents and web-pages, depending on the brand), however the two most popular formats are ePubs and PDFs. A third is Kindle’s proprietary format – KFX – which is used on Kindles only and is similar in functionality to an ePub – in fact, when you send an ePub (and most other file formats) to your Kindle, it will automatically convert it into KFX format.

The main difference between ePubs and PDFs is that ePubs are reflowable and PDFs have a fixed layout.

Essentially, what this means is that the reader has a lot of control over how an ePub is displayed on the screen, whereas with a PDF, the creator has the control.

ePubs are text-based files and the way that it is viewed can be customized by the reader. For example, when you adjust the font size, the text gets bigger and consequently less text can be displayed on the page. So the text that was at the bottom reflows onto the next page. The result is that ePubs do not have fixed page numbers that are absolute for all readers because someone using a smaller font may have five paragraphs on their page one, whilst another reader using a larger font has just two paragraphs on their first page, with the remaining three paragraphs on page 2 (if that makes sense!?)

In contrast, PDFs have a fixed layout for each page – every reader’s page one will look the same. This is useful for creators and authors who want to prevent their content from moving around on the page. For example, crosswords are often in PDF format because the creator wants both the grid and the clues to be displayed on the same page (and not reflow to the next page if the the reader changes the font size). In addition, the grid is an image rather than text, so cannot be reflowed. The alternative to changing font size on a PDF is to zoom in and out of the page.

Although I have used font-size in my examples, there are several other configuration options, such as font-family and line-spacing that are available with ePubs but not PDFs. There are also some configuration options solely for PDFs (such as zooming), but the main takeaway is that ePubs allow the reader to manipulate the layout, whilst PDFs have a fixed layout,decided by the creator.

SIDENOTE: It is possible to reflow some PDFs and some ePubs can have a fixed layout, so whilst these differences apply to the majority of cases, it is not always clear-cut.

As well as ePubs and PDFs, e-readers can open many other file formats including Word Documents, Comic Books (CBR, CBZ etc.), images (PNG, JPG etc.) and audio files (WAV, MP3 etc.). Supported file formats vary between brands.

DRM-Protected E-Books

It is possible to download a vast array of e-books from the Internet for free (particularly old classics, for which the copyright has expired and are in the public domain – see the Project Gutenberg library).

However, books that are still under copyright should be purchased from a digital book store to ensure that the author still gets their royalties.

When e-books first became popular, authors and publishers realised that it had massive potential to affect their revenues. There was nothing stopping one person from buying an e-book and sharing it with 100 other people. Instead of 100 sales, they would just get one. Of course, there are legal implications to sharing intellectual property without permission but this is difficult and costly to enforce.

And so they introduced Digital Rights Management (DRM). This is a method of restricting who can read an e-book, the idea being that only the person that purchased the book can read it and they cannot share it with their friends or make it available on the Internet. The ebook is tied to the purchasers user account and third-party software may be required to transfer the ebook to other devices. This same method is used by several public libraries to lend e-books.

Large e-reader brands with their own book stores (e.g. Kindle, Kobo etc.) provide a seamless DRM experience between their store and your devices. If you buy a book from the Kindle Store, it is almost immediately available across all your Kindle e-readers (including the Kindle app on your phone or tablet) without you having to do anything more. The same applies when you buy an ebook from the Kobo Store – it is available to read on all your Kobo devices and the Kobo app.

However, if you buy a DRM-Protected e-book from a third-party store, transferring it to your e-reader is a little more involved. To make the e-book viewable on your e-reader, you have to install a piece of software called Adobe Digital Editions (ADE) on your computer, then connect your e-reader to the computer via USB before commencing the transfer.

Similarly, if you purchase an e-book from the Kobo Store, but want to view it on a Pocketbook e-reader, you have to download the ebook (and accompanying licence file) to your computer and transfer it to your Pocketbook using ADE. In all honesty, it’s a bit of a ballache, but unfortunately it is the system that many publishers have chosen to protect their digital content.

A further complication is that not all e-readers support Adobe DRM, which means that it is not possible to read DRM-Protected e-books on a large number of e-readers. This means that you can be limited to which e-book stores you can buy from. Kobo and Pocketbook are perhaps the two biggest brands that support Adobe DRM (both for purchasing and viewing e-books).

Amazon Kindle is the biggest brand that does not support Adobe DRM. You cannot view any DRM-Protected e-books on a Kindle that were not purchased from the Kindle Store. Similarly, you cannot transfer any e-books purchased from Kindle to any non-Kindle devices. This is why many e-book aficionados say that Kobo gives its users a lot more freedom than Kindle. Kobo users are free to buy from any e-book store, whilst Kindle users are limited to Amazon’s store. However, this only applies to DRM-Protected content – Kindle does support viewing DRM-free e-books in a variety of file formats.

Another point of note is that although most Android-based e-readers do not support Adobe DRM, many allow the installation of third-party apps from the Google Play Store. So, it is possible to install the Kindle app or the Kobo app on an Android e-reader and read your books through the app – DRM-Protected e-books download directly into the app (and can only be accessed via the app itself).

SIDENOTE: Despite what I’ve said previously, it is possible (in some cases) to remove DRM from your e-books using a piece of software called Calibre Ebook Management (with the De-DRM plugin). This can also be used to convert e-books into different formats. Using Calibre is beyond the scope of this article and can be quite technical and involved, so I won’t go into any more detail – I just wanted to point out the possibility 🙂


In summary, e-readers suit people that enjoy reading but prefer a paper-like experience over a brightly-lit screen.

E-readers allow you to keep all your books in one place so that you can read them anytime and anywhere. And they allow you to adjust the layout and text to your preferences, as well as provide lots of useful additional tools, such as a dictionary and the ability to highlight passages of text.

The main file formats are ePub (reflowable) and PDF (fixed layout with each element ‘anchored’ to a specific area of the page).

Purchased e-books usually have DRM-Protection, which means that only the buyer can view them. When you purchase an e-book from the same store as your brand of e-reader, it downloads to your devices seamlessly. If you buy from a third-party store, you will have to use Adobe DRM to transfer your e-book to your e-reader (or in the case of Kindle you cannot transfer any non-Kindle DRM-Protected e-books to your e-reader or transfer your Kindle e-books to a non-Kindle device). Kobo and Pocketbook are the main brands that support Adobe DRM. Android tablets can access DRM-Protected e-books by installing the relevant book store’s app (e.g. Kindle, Kobo Pocketbook etc,).

I hope this has answered most of the questions that people new to e-readers want to know, but if you are unsure about anything, feel free to drop a comment below.


About the author

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Dan Dutton is passionate about E-ink writing tablets, which bring together the pleasure of writing on paper with the power of digital technology. When he bought his first tablet, he realised that there wasn't a lot of unbiased information available for people that were considering buying an E-ink tablet, and so he built eWritable.

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