This EPUB to AZW3 conversion does not run here
AZW3 is what many Kindle books use internally.
Creating AZW3 needs Kindle or Calibre tools. This page cannot build one.
What to do instead
Use AZW3 to EPUB when you have a Kindle file you are allowed to read elsewhere, or EPUB to PDF for a simple reading copy.
The page that does work is EPUB to PDF.
Why EPUB to AZW3 is its own job
EPUB to AZW3 sits on this site because EPUB and AZW3 are not interchangeable, even when they look similar in a file list. AZW3 is what many Kindle books use internally. EPUB is the copy to keep if you want the widest choice of reading apps. Kindle prefers its own formats. People convert AZW3 they own into EPUB so the book opens off the Kindle.
Creating AZW3 needs Kindle or Calibre tools. This page cannot build one.
The EPUB file you already have
EPUB is the open ebook format. Apple Books, Google Play Books, and most reading apps open it. A fixed, illustrated layout is simplified. DRM-locked books fail.
Keep the file you bought. Convert only books you are allowed to convert.
What a AZW3 result is for
The download has to be AZW3, because that is the format the next step named. People convert AZW3 they own into EPUB so the book opens off the Kindle. Reading the text out of a file you are allowed to convert is the useful direction.
DRM-locked Kindle books fail. Do not expect a print-accurate layout.
How to tell that EPUB to AZW3 worked
EPUB to AZW3 is worth using only when AZW3 is what the next step actually named. AZW3 is what many Kindle books use internally. What you get from EPUB to AZW3: Creating AZW3 needs Kindle or Calibre tools. This page cannot build one. Before you trust it: Use AZW3 to EPUB when you have a Kindle file you are allowed to read elsewhere, or EPUB to PDF for a simple reading copy. The file stays in your browser and is not uploaded. The limit is 100 MB. Keep the original until the download has been opened in the program that will use it. A second pass rarely helps. If the first AZW3 file is rejected, read the error from the program that rejected it. Another conversion of a bad result usually makes the file worse, not more compatible. When you are done, you should still have the EPUB original and one AZW3 download that you have opened. If those two are the same kind of failure, this was the wrong tool and the page above is the place that says so. Convert only a book you own and are allowed to convert. EPUB to AZW3 moves chapter text. A fixed illustrated layout is simplified, and DRM-locked files fail. Kindle formats can often be read here and not written. Keep the original ebook until the new file opens in the reader you actually use.
Here is the decision for EPUB to AZW3. You start with EPUB and you stop when a real program accepts AZW3. Chapter text you own can be repacked into EPUB or out of EPUB. This site does not write a new AZW3. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
Use AZW3 to EPUB when you have a Kindle file you are allowed to read elsewhere, or EPUB to PDF for a simple reading copy.
A related step, if you still need one, is AZW3 to EPUB.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.