Hi Gisella, if you mean through want to get a PDF into the iBook bookshelf, then try loading the PDF into Safari from a web page.. When it is loaded touch on the PDF and a menu will show up in the upper right hand corner. I think it says "Open In iBooks". If you get the PDF in an email, touch and hold the PDF icon in the email. A menu should pop up with the "Open In iBooks" choice.
If you are looking for something different please say and I'll try to help.