How do I upload all the books stored in iBooks to my google docs account?

You can't. Google Docs is not a file storage system, it's an online suite of productivity applications. If you mean Google Drive, you'd have to download the iBooks to your computer and then upload the files yourself manually. You can't use the iBooks in any other application or service, though, so copying them to Google Drive would only be useful for backup purposes.

Regards.

I did indeed answer your question. You cannot export books out of iBooks on your iPad to a third-party service. You will have to do this from your computer.

And again, no, Google Docs is not storage. You're apparently confusing Google Docs:

https://support.google.com/drive/bin/answer.py?hl=en&answer=143206&topic=21008&r d=1

with Google Drive.

https://www.google.com/intl/en_US/drive/start/index.html

unless Google themselves do not know their own services or leave major features out of their description of Google Docs.

Regards.

You can find the location of any file in your iTunes library by right-clicking on it and then using Show in Windows Explorer. iBooks that have been downloaded to your library will be stored at <Media Folder>\Books\<Author>. You can then copy these to any location of your choice using Windows Explorer, or the upload tools provided with your cloud service of choice.

As given, for iBooks purchased from iTunes there is unlikely to be any benefit to storing them in another location as you can already redownload directly from the store on demand, and such titles cannot be read except in the iBooks app on an iOS device.

tt2

You can read PDFs on your PC with Acrobat reader or an eBook reader that can also read this format along with unprotected ePub files. i believe the Kindle application can do so. You can move the files around just like any other file on your computer.

tt2

Ask Google Docs. Apple do not own that

When you sync your device you should find any books you have opened with the iBooks app end up being transferred to the <Media Folder>\Books folder in your iTunes library.

tt2