We want to know if you ever have difficulty running CircularFLO.
Please check the topics below or contact us to receive free support.

Locating the installer once downloaded

If the downloaded DMG disk image doesn’t open on your Mac. Please look for a file named ‘CircularFLO_installer.dmg’ in your browser’s download folder. Double click this DMG file to mount on your desktop or go to the Finder menu Go > Computer.

Making sure you have the required software

CircularFLO is a Mac only application (OS X 10.6 and later) and requires Adobe InDesign (version CS6 or CC). If you have more then one version of InDesign installed on your Mac then please close other versions and launch a single version of InDesign CS6 or CC prior to launching CircularFLO

For best results, close other applications and any InDesign documents before running and whilst running leave the Mac alone whilst processing.

Why did CircularFLO not generate a KF8?

The Amazon KF8 format is not a sophisticated as the fixed layout EPUB3 and does not yet support the addition of audio, video, animation or read aloud text highlighting.


So, when any of these CircularFLO Pro features have been added to a book, CircularFLO only produces the EPUB file and does not produce a KF8.

If you would like to produce a KF8, please delete or merge the layers containing audio, video, animation or read aloud information and run CircularFLO again. You will not be charged more than once to make the same eBook.

Sending us the run log

On the rare occasions when the CircularFLO processing has been interrupted then the ‘run log’ file is very useful. It will show us where in the process things have stopped.

The run log is a small text file named ‘run_log.log’ and it can be found from the CircularFLO menu



If you are experiencing a problem and have a run log to share, please attach to an email to our support team with a short description of the problem and a screenshot of any messages shown. 

To email a run log open in the Mac Console application please choose to attach to an email from File menu > Mail


The full path to the run log is your User Folder > Library > Application Support > CircularFLO. Please note this is your USER folder Library which is different to your Macintosh HD Library.
The run log does not contain any personal information.

Sending files with wetransfer

Please do not email large files.

If you are asked too, please zip and send files to us via wetransfer.com use the email help@circularsoftware.com for reference.

If your files are over 2GB then transferbigfiles.com is a good alternative.

Installing Java to run EPUB validation

In order to check that your EPUB is complete and ready for submission to retailers we run a validation. See the Understanding EPUB validation below for more.

This validation uses Java which is no longer bundled with later versions of Mac OS X and so to use this feature we require a one time installation of Java. This is freely available from here and this is the same page that Apple also direct users to in order to get Java installed.

Understanding EPUB validation

The fixed layout EPUB3 files that CircularFLO produces are validated automatically as part of the process. We use the latest EPUB3 EpubCheck to do this.

As the process is automatic it is rare that an EPUB will not validate but if it does then you will be alerted and the run_log will be shown next to the EPUB. Open the run_log in TextEdit and at the bottom you will see the error report,

There is usually a simple reason but unfortunately the simple reason can be hidden in a difficult to understand and scary looking report.

This site helps to decipher what the report means. The most common reason we find is a ‘required elements missing’ error caused by hyperlinks pointing to none existent page.

If you are having trouble understanding a EPUB check report then please email the run_log to help@circularsoftware.com

If you would like to validate an EPUB yourself outside of the CircularFLO process we recommend the free tool pagina EPUB-Checker.

Converting to KF8 using Kindle Previewer or Kindlegen

CircularFLO can create a fixed layout KF8 directly from the fixed layout EPUB3 produced. By dragging the EPUB file onto the free Kindle Previewer you will convert and open the KF8. The converted file is placed in a folder ‘Compiled-content’ next to the EPUB file. Note: you will always see warnings when converting this way due to the EPUB3 code used which is not recognised as part of the KF8 format, this is normal and does not affect how the KF8 file will work. 

Alternatively your EPUB3 can be converted to KF8 automatically as part of CircularFLO’s eBook creation process if Kindlegen is present on your Mac. Kindlegen is a free download and available here.

Although the .mobi files seem very large when compared to the EPUB files, this extra size is removed again once the book is distributed by Amazon.

Previewing KF8 files on a Kindle Fire device or a Mac

Although we recommend sending the .epub file to Amazon, CircularFLO can also generate a .mobi for ‘side loading’ onto a Kindle Fire device or viewing your book on a desktop computer.

The best way to preview your KF8 file is to side load onto a Kindle Fire device. A good link about doing this is here.

Another way to view you KF8 is to open it in your Mac/PC using Kindle Previewer

Note: Amazon do not (yet) provide a way to preview your KF8 file using their Reading apps.  Your published book WILL be available for purchase and viewing as expected once in their Kindle Store however there is currently no way of previewing the file in the Kindle Reading apps for Android or the iOS (iPad and iPhone). The ‘Send to Kindle’ app does not work for fixed layout KF8 and the ‘Kindle’ app for Mac OS gives a different reading experience and does not support comic zoom.

Understanding KF8 validation

The automatic KF8 conversion will only be carried out on valid EPUB3 file from CircularFLO so it is rare that a valid KF8 will not also be made.

If the process fails you will be alerted and the run_log will be shown next to the EPUB file.

On the rare occasion that a conversion fails it is usually due to hard to compress images when using the KF8 text zoom mode. The run_log will show the name of the image but if you are having trouble understanding a Kindlegen report then please email the run_log to help@circularsoftware.com

Unzipping and Zipping EPUBs

Sometimes it may be useful to open your EPUB3 folder to add extra functionality or to add or amend the code or content.

For those curious enough to look into the code we recommend these epub-applescripts to be sure to open up and repack the EPUB correctly.

Rules when making updates

After the initial purchase and processing on an eBook with CircularFLO you are then able then make unlimited updates to your eBook without charge.

In order to protect this from misuse there are some restrictions in place:

  • Files need to remain together with the original InDesign book
  • Files need to be the original ones used with the original book. They can be modified and saved but not ‘saved as’ into new documents.
  • New files can NOT be added to an existing book
  • Files within a book can be updated and new pages added or removed
  • Files can be removed from a book

If you are having genuine difficulties remaking a pre-purchased book then please contact us.

Any questions? Check out our Frequently Asked Questions page or Contact page with questions and comments or for support and updates.

Mac, Mac OS, iPad, iPhone, iPod, iPod Touch, iTunes, iTunes Connect, iBooks, iBooks Author, iBookstore are registered trademarks of Apple Inc. • Adobe, Adobe Creative Suite, Adobe InDesign, Adobe Photoshop and Adobe Illustrator are either registered trademarks or trademarks of Adobe Systems Incorporated in the United States and/or other countries. • Amazon, Amazon Kindle, Kindle Fire, Kindle Previewer and Kindlegen are re either registered trademarks or trademarks of Amazon.com, Inc. in the United States and/or other countries.