Apple’s tablet comes with the company’s iBooks app installed by default.
You only need to download the appropriate app.
Any ePub digital book can be opened in the Books app or in other downloadable apps.

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ePub
The ePub open format is one of the most commonly used e-book file types.
Several programs for Mac and Windows convert other kinds of e-books to ePub format.
Barnes & Noble Nook
Barnes & Noble sells e-books on its website and through itsNook app.
Access these books using the free Nook app available at the iPad App Store.
Nook e-books are a renamed version of the common ePub file pop in.
Read Kindle books on the iPad using theAmazon Kindle app.
Kindle e-books are a modified version of the Mobipocket file format and use the AZW file extension.
There are tons of PDF-compatible apps for the iPad, includingAdobe Acrobat Reader, GoodReader, and iBooks.
comiXology
Amazon’scomiXologyis the leading online comics and graphic novel store.
KF8
Kindle Format 8 is the next-generation version of the Kindle e-book file.
It adds support for HTML and CSS to the existing Kindle format and uses the .AZW3 extension.
The Kindle app on the iPad supports the KF8 format.
Microsoft Word
Microsoft Word creates .docx files.
Some e-books, usually those sold as direct downloads by self-publishers, come in this format.
Outside of the Kindle, though, you likely won’t encounter it too often.
Then read them in iBooks or another ePub-compatible reader app.
A large number of apps support plain text files, including the paid app GoodReader, and iBooks.
Some of the most common audiobook types supported by the iPad include: