Absolutely. But, note that eBooks are sold as .PDF files, and not in any specific eReader file type (each eReader uses a different file type, so it would be impossible for me to address all of the various devices and file types out there).
Most eReaders can accommodate these files, they just might not be perfectly formatted to look as good as a file that was made specifically for that device (for example, the font might be slightly small), but most of them should be readable regardless.
For the ones that aren’t, they can all still be read on your computer with the use of a Preview program, or whatever you usually use to view .PDF files.
For Kindle, you can use the “Send to Kindle” app. It works on PC or Mac. It can send the ebook (once it is downloaded) to your Kindle app on your Apple device (ie. iPad or iPhone), Android device, or Kindle. Visit this tutorial for further instructions.