I could said the document could feature is very convenient. I could read PDF ebook in my desktop and then upload to the document could. Then, I could read the same ebook in my cell phone.
What OS version are you using?
Try reinstalling the application after changing the language back to english?
Thanks for reporting the issue. We are working on a fix for the same and shall try to incorporate it in one of our future releases. As a workaround, you can open the PDF file that you want to read directly from the file manager. We regret the inconvenience caused.