South Korea's Samsung proposed an initial price range of $13.35 to $15.49 per share, which represents a premium of 38 percent to 60 percent over BlackBerry's current trading price, the source said.
The offer price would imply an enterprise value of $6 billion to $7.5 billion for BlackBerry, assuming conversion of $1.25 billion of convertible debt, according to the documents.
Representatives from the two companies, which are working with advisers, met last week to discuss a potential transaction, the source said, asking not to be identified because the conversations are private.
Representatives for BlackBerry declined to comment while Samsung could not be immediately reached for comment.