Ebook converter online free: convert EPUB, MOBI, PDF, and AZW in your browser

Convert your ebook files between EPUB, MOBI, PDF, and AZW formats with ToolHQ's ebook converter, your file never leaves your device.

An ebook converter changes a digital book from one format to another so you can read it on your preferred device or app. The same book might be a MOBI file from one source and an EPUB from another, but your reader only opens one of them.

Most online ebook converters require you to upload your file to a remote server. For personal libraries, purchased ebooks, or documents you converted from notes, that upload creates an unnecessary copy of your files on someone else's server. ToolHQ's converter processes everything locally in your browser, so your books stay on your device.

Key takeaways

• ToolHQ converts between EPUB, MOBI, PDF, and AZW entirely in your browser
• Your file never leaves your device, no upload, no server, no file size limit
• EPUB is the open standard supported by all readers except stock Kindle
• AZW and MOBI are Kindle-native formats; newer Kindles now support EPUB directly
• Free with no account required

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Ebook formats explained: what each one is and where it works

The ebook format landscape has four major players, each tied to a different platform or purpose.

EPUB is the open standard published by the W3C EPUB specification. It is the universal format: Apple Books, Kobo, Google Play Books, and most reading apps on Android and iOS all support EPUB natively. Since 2022, even newer Kindle models (Kindle Paperwhite, Kindle Scribe, and Kindle app) support EPUB directly. If you want a single format that works almost everywhere, EPUB is it.

MOBI is an older format developed by Mobipocket and acquired by Amazon. Kindle used MOBI as its primary format for years. While Amazon phased out MOBI support in 2022 (replacing it with AZW3/KFX for new content), many older ebooks and sideloaded files are still in MOBI format. Most Kindle devices can still open MOBI files.

AZW and AZW3 are Amazon's proprietary formats. AZW is the older Kindle format (essentially DRM-wrapped MOBI). AZW3 (also called KF8) is the newer format supporting richer formatting, CSS, and embedded fonts. If you downloaded a book from the Kindle store, it is likely AZW3.

PDF is the universal document format, good for fixed layouts (textbooks, comics, technical manuals) but often poor for ebooks because text does not reflow to fit different screen sizes.

Format	Open standard	Best for	Kindle support	Other readers
EPUB	Yes (W3C)	Universal reading, newer Kindles	Yes (2022+)	Excellent
MOBI	No (Amazon)	Older Kindles, sideloading	Yes (older devices)	Limited
AZW / AZW3	No (Amazon)	Kindle store content	Native	Limited
PDF	Yes (ISO)	Fixed-layout documents	Yes (small screens are hard)	Excellent

The Wikipedia article on EPUB covers the format's development history and specification versions if you want technical detail.

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When you need to convert an ebook format

The most common scenarios where format conversion matters.

Reading a MOBI or AZW file on a non-Kindle device: If someone sends you a MOBI file but you read on Kobo or Apple Books, you need EPUB. Convert the file and import it to your reader.

Sideloading to an older Kindle: Older Kindle models (pre-2022) do not support EPUB. If you downloaded an EPUB from a library or project Gutenberg, convert it to MOBI first.

Archiving your library in a standard format: Personal ebooks purchased from various stores might be in AZW, EPUB, or MOBI. Converting everything to EPUB gives you a consistent archive that will work on future devices.

Converting a PDF to a readable ebook: PDF works on large screens but is difficult to read on a phone or e-reader. Converting a text-heavy PDF to EPUB allows the reader to reflow the text and change the font size.

Sharing a document as an ebook: You wrote a guide in PDF but want to distribute it in a format that reads nicely on phones. Convert to EPUB.

Daria, a graduate student, had downloaded 40 academic books for her dissertation research. Half were in EPUB, a quarter were PDFs, and the rest were in various formats from her university library. She read exclusively on a Kobo Clara. She used ToolHQ's ebook converter to batch convert the PDFs and oddly-formatted files to EPUB, then loaded them onto her Kobo. Every book opened with properly reflowed text, adjustable fonts, and night mode support. She saved roughly three hours of reformatting that she would have spent zooming in on fixed PDF pages.

Convert your ebook now, no upload, no account required

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How to convert an ebook with ToolHQ

1. Open the tool. Go to https://www.toolhq.app/tools/ebook-converter.

2. Select your file. Drop in your ebook file or click to browse. Accepted input formats: EPUB, MOBI, AZW, AZW3, PDF.

3. Choose the output format. Select the format you need from the dropdown.

4. Convert. Click Convert. The browser processes the file locally, no file is sent to a server.

5. Download. The converted ebook downloads automatically or appears as a download link.

Because conversion runs locally, there is no server queue, no file size restriction imposed by a free tier, and no copy of your file created on a third-party server. Your file never leaves your device.

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EPUB vs. MOBI vs. AZW: which should you use?

The right format depends entirely on your destination device and use case.

Go with EPUB if: You read on anything other than an older Kindle. EPUB is the open standard, has the widest device support, is the format libraries distribute, and is what most ebook storefronts other than Amazon use. Newer Kindles read EPUB too, so EPUB is increasingly the one format that works everywhere.

Go with MOBI if: You are sideloading to an older Kindle (pre-2022 model) that does not support EPUB. MOBI is widely supported by Kindle devices and is the standard for self-publishers distributing via Draft2Digital or Smashwords to older Kindle readers.

Go with AZW3 if: You are creating Kindle-optimized content with rich formatting, custom fonts, and complex layouts. AZW3 supports more CSS features than MOBI.

Go with PDF if: The layout must be fixed regardless of screen size, forms, certificates, image-heavy magazines, technical schematics. PDF is not ideal for reflowable reading on small screens.

Kenji, a self-published author, had released his novel as an EPUB on his website. A reader emailed saying they could not open it on their older Kindle Paperwhite. Kenji used ToolHQ's ebook converter to create a MOBI version from the same EPUB. He uploaded both formats to his website download page and added a note recommending EPUB for most readers and MOBI for older Kindles. Support emails about incompatible formats dropped to zero.

For related tools, the PDF compressor reduces PDF file size before converting, and the archive converter handles ZIP and other bundle formats your ebooks may arrive in.

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Frequently asked questions

Can I convert a DRM-protected ebook?

DRM (Digital Rights Management) protection prevents conversion. ToolHQ's converter works only on DRM-free ebooks. Ebooks purchased from Amazon or Apple typically have DRM. Library-borrowed ebooks and books from Project Gutenberg are usually DRM-free.

Will converting EPUB to MOBI preserve formatting?

Simple formatting (bold, italics, chapter headings, paragraph breaks) converts well between EPUB and MOBI. Complex layouts, custom fonts, and CSS-heavy designs may not convert perfectly, as different formats have different CSS support levels.

How large can the ebook file be?

Because processing is local, there is no server-imposed size limit. Ebooks are typically small files (under 10 MB), so this is rarely a constraint.

What is the difference between AZW and MOBI?

AZW is Amazon's format built on MOBI with added DRM encryption. AZW3 (also called KF8) is a newer Amazon format with better CSS support. If you have a DRM-free AZW file, it is often functionally identical to MOBI.

Can I convert a PDF ebook to EPUB and have it reflow properly?

Text-based PDFs convert to reflowable EPUB reasonably well. PDFs with complex column layouts, embedded images as text, or scanned pages convert poorly. OCR-based PDFs (where text is an image layer) will produce garbled output.

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The short version

Ebook format incompatibility is one of the most frustrating parts of building a digital library. EPUB is the universal open standard, MOBI and AZW are Kindle-native, and PDF locks layout at the cost of readability on small screens. ToolHQ's ebook converter handles all four in either direction, entirely in your browser.

Your file never leaves your device, a meaningful privacy advantage over every server-based converter.

For related workflows, see the PDF to Word converter if you need to edit a PDF-formatted ebook, or the archive converter for unpacking ebooks delivered in ZIP files.

Convert your ebook free, browser-based, no upload, no account

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