If you purchased ebooks from a seller other than Amazon on your iPhone or iPad, you can download the books and save them to the Files app or other third-party file managers you are using, then tap one of these share buttons found in these files apps, choose Send to Kindle option in the share menu to send books to the Kindle app for iOS. This method however can’t help you send any files that are over 50MB, or archive them in Kindle Library. As a result, you have to open and read those books using a third-party book reader, such as KyBook, or export these large books or files from the iPhone or iPad to your computer or Kindle, or import those large books from computer to iPhone or iPad using iTunes which can bypass the Send-to-Kindle file size limit.

There are different methods to transfer books from iPhone to PC or Kindle. Today, we will introduce the Snapdrop free file transfer which can help us with local file sharing across Windows, Mac, iPhone, iPad and Android.
Unlike other file sharing apps, Snapdrop is a progressive web app for local file sharing. You don’t have to download or install an extra app on your iPhone, iPad or PC. You can use your web browsers instead. Simply visit snapdrop.net on iPhone or iPad and your Windows or Mac computer. Your phone and/or computer can be discovered by every other devices on the same network. If not, make sure to connect them to the same Wi-Fi network before accessing the Snapdrop website from your browsers.
On your iPhone or iPad, tap on the name of your computer, a dialog pops up with options to select files from Photo Library, Files or take new photos and videos and then share with your computer.

Here we choose Browse, then the browse through the files and folders saved on your iPhone or iPad. Find the books or files you like to send and transfer it to your computer.
On your PC or Mac, your web browser may automatically download the file or ask you to choose a location to save it depending on your browser setting.