How to make PDF appear as a book in iBooks

My mother has an iPad. She is not what you'd call a computer geek, so she somewhat struggles with it. I got her a good PDF file that explains how to use an Ipad but the problem is that when I upload it to her iPad this PDF disappears from her iBooks layout and one needs to switch to PDFs on top to open it. [Translated into my mother's language] -- it will be unreachable.

So my question is, how to make a PDF appear in the books section in iBooks?

PS. I read somewhere that one needs to convert it to epub format. If so, how can I do it? It doesn't seem to be as easy as it sounds. I tried out one free online converter and it made a mess out of this PDF. Is there a simple 1-to-1 converter?