The problem with ebook file formats is that there are a dozen of them and not all of them are compatible with all e-readers. Why should you convert an ebook to a PDF? This makes ebook formats generally superior to PDFs for this task. There are many different types, but they all were created with the sole purpose of reading a book on a screen. However, the PDF standard was not designed with e-readers in mind and will therefore lack some of the ebook-specific features you would expect.
This means you could send a PDF to your Kindle and read that document. The format is compatible with most e-readers, including the popular Amazon Kindle series. It allows you to create, view, and share pages of documents across many platforms. A PDF is a document format compatible with most devices and operating systems.