Moved to InDesign EPUB forum.
You can't do it directly. Assuming you haven't got the original InDesign file, and you want to create a reflowable text ePub, you'll need to extract the images and text from the PDF and start again using paragraph and character styles, anchoring the images and so on. If it's "complex" you made need to simplify the design, or consider producing a fixed layout ePub, which you can produce with InDesign CC. The Kindle uses it's own format.
Thank you for your answer Derek. No I don't have the original indesign files.
What would be the best way to extract from the PDF or is there a shortcut way to convert a PDF into an indesign doc easily that might keep character and paragraph formatting? I have tried pasting it in word and then transferring it to inDesign but then it is just a mass of unformatted text which is quite a lot to go through.
And can you tell me how I should go about setting up the correct inDesign file to work in and prepare for an ePub export?
To extract the content from your PDF in a form to work on in InDesign
Open the PDF in Acrobat
For the images: Under Document processing you can “Export All Images”.
For the text: Save as > Text Plain
To create your ePub, place the text in In InDesign you will need to create Paragraph and Character Styles and format the text with these, anchor the images within the text, create a TOC and so on. You need to regularly export to ePub (Reflowable) as you go to check all is going well, and also check you file with the IDPF validator: EPUB Validator (beta)
You can learn how to do all this properly by taking the online Lynda course: http://www.lynda.com/EPUB-tutorials/InDesign-CC-EPUB-Fundamentals/143324-2.html
Which will also show you how to subsequently convert your ePub into a mobi file, which is the format used for the Kindle.
I suggest you produce a couple of smaller practice ePubs first so as to get the hang of it!