IPad – Exporting highlights from Kindle Personal Documents to a TXT file

There are two main categories in Kindle App for iPad:

• Books – contains books purchased from Amazon; highlights are available at https://kindle.amazon.com/your_highlights — it works fine for me.
• Personal Documents – contains all other books; highlights are not available online.

So, I have book purchased at different source than Amazon and I would like to be able to export my highlights and notes to a text file (or any other common format). My approaches so far:

• As far as I know, https://kindle.amazon.com/your_highlights is available for Books category and thus, for Amazon-purchased books only. There are no entries from "Personal Documents"
• I cannot move my book from Personal Document to Books – there is no such option in Kindle App. There is no such option on Amazon's "Manage Your Kindle" site too.
• There is no option to export all highlights. Kindle app has option to share a highlight via Facebook or Twitter, but there is no option for copy or export it.

I synced my book with Kindle Touch and highlights are synced successfully. But:

• There is no export option in Kindle Touch too.
• I am unable to read highlights content on my cpu. The file with highlights has extension .azw3r and contains relative references, for example: annotation.personal.highlight 283390 283606.
• There are no entries in My Clippings text file (there are entries there but for non-synced books).

The question is: How can I export my highlights and notes from iPad Kindle App to a TXT or any other common file?

Note I'm using Windows but I put this question to Apple.SE since the root problem comes from iPad.