If you have an ebook file that won't open on your device, the free desktop software calibre will convert it to EPUB, MOBI, AZW3, or PDF without asking for an account or a credit card. For source material you can legally convert yourself, Project Gutenberg offers public-domain ebooks in multiple formats, also free and without registration. Those two services are the only documented, legitimate answers here that meet every condition you typed.
What Each Format Is For
EPUB is the standard for almost every ereader except Amazon's Kindle. calibre’s own FAQ says EPUB is the preferred output for normal Android devices, and Project Gutenberg recommends EPUB for "almost all ereaders, smartphones, and tablets." MOBI is an older Amazon format; calibre’s FAQ says MOBI is for Kindles. AZW3 is Amazon’s newer format, also for Kindles, and calibre can output it directly. PDF is a fixed-layout format that works on any screen but does not reflow text. Project Gutenberg generates its PDFs from LaTeX, meaning they are computer-made derivatives, not scans of a printed page.
What Conversion Loses
No conversion is perfect. calibre’s documentation says the software tries to make the output as close as possible to the input, but layout-heavy features, tables, images with precise placement, multi-column text, will not carry over perfectly. For PDF output, calibre’s own help notes that it removes headers and footers and reflows the content, which means you lose the original page numbers and any marginal notes. Project Gutenberg states that its MOBI files are "automatically generated derivatives" of the EPUB, and its PDFs are generated from the same source HTML and plain-text files. That means the PDF is not a preservation of an original print layout; it is a fresh document built from the same text. If you need exact page reproduction, you will not get it from these tools.
The Two Services That Work
calibre (Desktop Software)
calibre is a free desktop program that converts ebooks between EPUB, MOBI, AZW3, and PDF, plus many other formats. It does not require an account or a credit card. The documentation does not describe a paid tier or a country restriction. It is free open-source-style software, though the retrieved pages do not explicitly state a license. To use it, you download the program to your computer, add your ebook file, and choose an output format. The conversion happens locally, so nothing is uploaded to a server. If you already own an ebook in a format your reader cannot open, calibre is the documented answer.
Project Gutenberg (Source Files)
Project Gutenberg is a free archive of public-domain ebooks. You can download books in EPUB, Kindle/MOBI-style formats, and generated PDF without creating an account or entering a card number. The retrieved pages do not list a country restriction for downloads. The site only accepts works that are in the public domain in the United States, and its ebooks are generated from master HTML and plain-text source files. If you want a book to convert, this is where you get the legal source file. The EPUB is the recommended format; the MOBI and PDF are derivatives and may not match the EPUB exactly.
What to Check Before You Commit to a Format
Check what your device actually supports before you convert. If you have a Kindle, you want MOBI or AZW3. If you have a Kobo, Nook, phone, or tablet, you want EPUB. If you need to print the book or keep a fixed page layout, PDF is the choice, but expect the text to look different from a printed book. If you are converting from a PDF, expect the output to lose the original page breaks and any two-column layout. calibre’s documentation warns that PDF input is the hardest to convert cleanly because PDF stores visual positions, not text structure.
What Is Not Worth Your Time
Online converters that promise to handle EPUB, MOBI, AZW3, and PDF without an account are not documented here as legitimate, official free services that also state their account, card, and country terms clearly. The retrieved pages for bookconv.com, converthub.com, and bookize.com do not provide the same level of documentation about format loss, account requirements, or country restrictions that calibre and Project Gutenberg do. Stick with the desktop software and the public-domain archive.
Frequently Asked Questions
Can I convert a book I bought from a store?
If the book has no copy protection (DRM), you can convert it with calibre. If it has DRM, calibre cannot remove it, and this article does not describe how to bypass that protection. You would need to check whether the store offers a DRM-free download or whether the book is available from Project Gutenberg.
Will the chapter headings and images survive conversion?
Most chapter headings and standard inline images survive. calibre preserves the text structure, but images that are placed in a specific position on the page, or tables with complex formatting, may shift or break. The documentation says the software tries to make the output close to the input, but layout-heavy features are not guaranteed.
Does Project Gutenberg have every public-domain book?
No. Project Gutenberg only accepts works that are in the public domain in the United States, and the books are submitted by volunteers. Many public-domain books are not yet in the archive. You can search for a title, but if it is missing, you will need another legal source such as Open Library or Standard Ebooks.
Can I convert a PDF to EPUB without losing the page numbers?
No. calibre’s PDF conversion removes headers and footers and reflows the text. The original page numbers are lost because the EPUB format does not have fixed pages. If you need page numbers, keep the PDF.
Is calibre safe to download?
The software is documented as free and open-source-style, and the official site is manual.calibre-ebook.com. Download it from that domain. The documentation does not describe ads, tracking, or paid tiers in the software itself.
Free tools for this: Word.now, Pdfbear.com.
Where this fits
This is one guide from Where to Download Free Ebooks Legally.
