This will depend on the type of media you use to view the eBook; here's a list with some commonly used devices:
- PDF to Tablet (iBooks, etc.): PDF files on iPad or Tablet devices will open directly as a PDF; no need to unzip or extract the file before downloading your purchase.
From an iPad or iPhone: Download the PDF using your iPad or iPhone. Once the file fully downloads and is open inside of Safari, click on the blue "Open in iBooks" text in the top right. The eBook will automatically open up in and be added to your iBooks library. You can also select "Open in" to add the eBook (PDF file) to another application of your choosing.
Note: If you don't see that option, then tap once in the middle of your screen for it to appear; you may need to click on the "More" button on the top-left to locate the "Import to iBooks" option.
From a Computer: If you download the file on your computer and want to transfer it to a tablet, I suggest using a cloud-based storage system, such as Dropbox or Google Drive. Once you have the file synced to your tablet, open it up and then select the option to "Open in iBooks" (or the PDF viewer of your choice). Here's a link to more info on the Apple support website: http://support.apple.com/kb/HT4227
- ePUB to iPad: To add an ePUB file to iBooks, you'll need to do this through iTunes by adding it to your library. Here's a link with more information: http://www.apple.com/itunes/inside-itunes/2010/04/using-itunes-to-add-epub-files-to-ibooks.html
- MOBI to Kindle: To transfer a MOBI file to your Kindle device, you will connect it to your computer via USB. Here's a link with more information over on Amazon's website.
- ePUB to Nook: To transfer an ePUB file to your Nook device, you will connect it to your computer via USB. Please head over to the Barnes & Noble website with more specific information on adding files to your device.
- PDF to Kindle: Please use this link to learn how to transfer your PDF file to a Kindle device.
For information on your specific device, please check with the manufacturer's website or contact their support.