Related

EPUB unless you have a reason not to. It reflows to your screen and font size, keeps the table of contents, and every device in this list reads it. Every book in this library offers EPUB except a few Internet Archive scans.

Format	Take it when
EPUB	Default. Kobo, Nook, Boox, phones, tablets, and Kindle via Send to Kindle.
Kindle (KF8)	Only for sideloading over USB to a Kindle, and only if Send to Kindle is inconvenient. Project Gutenberg calls this file .kf8.images.
Plain text	Searching, quoting, or re-typesetting. No formatting, no chapters, tiny file. The right starting point if you intend to reprint.
PDF	Last resort. It is a fixed page image — it will not reflow, and on a six-inch screen it is close to unreadable. Some Internet Archive scans offer nothing else.

Amazon's Send to Kindle accepts EPUB and converts it on Amazon's side. Per Amazon's help page the accepted types are PDF, DOC, DOCX, TXT, RTF, HTM, HTML, PNG, GIF, JPG, JPEG, BMP and EPUB. MOBI is no longer on that list — do not go looking for MOBI files, and ignore any guide that tells you to.

Three ways in, all free:

1. Web. Go to amazon.com/sendtokindle, sign in, drag the EPUB in. Simplest option and the one to try first.
2. Email. Every Kindle has its own @kindle.com address, in Manage Your Content and Devices → Preferences → Personal Document Settings. Attach the file and send it. You must first add the address you are sending from to the approved sender list on that same page, or Amazon silently drops it.
3. USB. Plug the Kindle in and copy the file into the documents folder. Use the .kf8.images file from Project Gutenberg for this rather than the EPUB — older Kindles will not open a raw EPUB off the filesystem.

Two things worth knowing. Sent documents land in Docs rather than in your book library, which is a different tab on the device. And a converted personal document keeps your reading position and notes across devices, but it is not a purchased book — it will not appear in every Amazon interface the way a bought title does.

Plug it in over USB and copy the EPUB onto the device. That is the whole procedure. Kobo also reads EPUB from an SD card, and Kobo devices sold since 2023 will open the file without conversion.

• iPhone / iPad — Apple Books opens EPUB directly. Tap the downloaded file and choose Copy to Books.
• Android — Google Play Books imports EPUB and PDF, or use a dedicated reader such as Moon+ or KOReader.
• Any platform — the Kindle app reads whatever you sent through Send to Kindle, so the same file works everywhere you are signed in.

Calibre is the free desktop program for this, and it is the standard answer for anything the table above does not cover. It converts between every format here, fixes broken metadata, edits covers, and manages a library. Use it when you want to turn a plain text file into a properly chaptered EPUB, which is the usual first step in making a public-domain reprint.

• The Reading Room — the library.
• Book Archives — where the files come from.
• Public Domain Books — what you are allowed to do with them.