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Do you mean PDF???

Sync via iTunes (apps tab scroll all the way down) or open in safari or mail and opt to send to ibooks.

Dropbox will probably let you send to ibooks as well.
 
Goodreader works too. Grabbed a PDF via good reader web download hit edit open with iBooks and it's there. Works on ipad too.
 
in my ibook.. i don’t have the option to selection books or PDF as it shown on the top of the ibook? why is that?
 
how do i get the pdf in there? i use mbox for my e-mail?

do i send them in there?
 
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