Convert MOBI to PDF

Mobipocket published the format in 2000 for Palm handhelds and early phones, and Amazon bought the company in 2005 and built the first Kindles on it. For two decades it was how a book got onto an e-reader, which is why so many of them are still sitting in download folders and backup drives.

It stopped being current in 2022, when Send to Kindle stopped accepting it in favour of EPUB. Books already on a device keep working and sideloading over USB still works on many older Kindles, but nothing produces new MOBI files and nothing on a laptop opens one without help. That is the situation this conversion exists for.

This is the whole trade and it is worth being blunt about. A MOBI contains chapters of markup, and the reading software decides where one screen ends based on the device and the type size the reader chose. Two people reading the same book see different amounts of it, and page numbers in an e-book are estimates.

A PDF is a fixed number of fixed sheets. Converting therefore means choosing a page size, a typeface, a size and margins, laying the entire book out once, and freezing the result. That is an authoring decision made by a machine, and it is why the same book converted by two tools produces two different page counts and neither is wrong.

Add the file to Calibre and ask it to convert. DRM encrypts only the text records, so a protected book still shows its title and cover in the library — the cover proves nothing, and the conversion is the test. If Calibre stops with a DRM error, no converter will get past it either.

That check is worth doing first because the failure otherwise arrives at the end of an upload rather than the start. Plenty of MOBI files have no protection at all — books from authors and publishers who declined to apply it, files you made yourself, material sideloaded from elsewhere. Removing DRM is a separate question whose legal answer differs by country, and it is not something done here.

Later MOBI files contain the book twice. Alongside the original content sits a KF8 section — the AZW3 generation, with real CSS — so that a modern Kindle could use one and a 2008 device the other. Both are in the same file and a converter has to choose.

A tool that reads the older section produces a book stripped of styling that was present all along, and on anything more elaborate than plain paragraphs the difference is obvious. Calibre picks the better section; simpler converters do not always. If a converted book looks unexpectedly bare, this is usually the reason rather than the source file being poor.

The original MOBI generation is HTML of roughly 1997 vintage: bold, italic, a few heading levels, simple images, and no real stylesheet support, embedded fonts, tables or fixed layouts. For a novel that was always sufficient, which is why the format lasted twenty years.

It means a converted novel comes out looking generic — reasonable text, chapter breaks in the right places, and none of the typographic character a modern e-book would have carried. That is not a fault in the conversion. There was nothing else in the file to translate, and a converter that produced something elaborate would be inventing it.

Unless you are printing the book or marking it up, converting a MOBI to EPUB serves you better than converting it to PDF. EPUB reflows, so the reader chooses the type size; it is an open standard read by essentially every application and device; and Send to Kindle accepts it directly, which closes the one gap that used to justify keeping Amazon formats around.

PDF earns its place in three cases. Printing, because no e-reader prints. Annotation, because everyone can open and mark up a PDF. And handing a book to somebody whose machine has no reading software at all, where a PDF is the format that needs no explanation.

A book laid out at A4 or Letter is right for printing and poor on a phone, where every line has to be panned or the type becomes unreadable. That is the experience reflowable formats were invented to end, and converting to PDF brings it back.

If the PDF is for a tablet or a phone, choose a smaller page and a larger typeface before converting. A page roughly the size of a paperback with generous type produces something genuinely comfortable, where a shrunken A4 page does not. The decision has to be made going in; nothing about it can be adjusted afterwards.

Old libraries are rarely one book. Convert a single title first, open it, and look at the chapter breaks, the table of contents and the metadata before doing the other four hundred — author names in particular were filled in loosely across the format’s history and sort badly in a library view.

Where a conversion is done through this site it will run on a server rather than in the browser, because an e-book needs a real conversion engine. The free ceiling for server conversions is 25 MB per file, which is generous for a book and reached mainly by illustrated titles, and the working files are deleted as soon as a job finishes.

Keep it until you have checked the conversion, then stop treating it as the copy that matters. It is a delivery format for devices Amazon has moved on from, and its only remaining advantage is that an ancient Kindle will read it over USB.

The copy worth keeping is an EPUB, with a PDF beside it if you produced one for a specific purpose. That is the version that will still open in ten years, on hardware nobody has designed yet — which is the entire argument for doing the conversion while a tool that understands the format is still maintained.