Factual error: When Ewan McGregor drives to Belmont MA to visit Paul Emmett, he checks the mailbox to see whose mail it's addressed to. It shows the name Paul Emmett, address, Belmont MA 02324, which is the wrong zip code; it is the zipcode for Bridgewater MA, and Belmont MA should be 02478.
Factual error: Lang refers to 'The Times of London'. A British person talking to other British people, as he is, would always refer to Britain's premier newspaper by its correct title 'The Times'. Only foreigners call it 'The Times of London' to distinguish it from, for example, 'The New York Times' or 'The Times of India'.
Answer: Who would want him dead? Ruth, for one, as well as Professor Emmett (her CIA recruiter) and others involved in the conspiracy. Yes, the book had been published, but the secret message only comes across if one is in possession of all the knowledge that the writer had acquired, which the casual reader would not have. And minutes is plenty of time for Ruth, Emmett, or anyone else to make a phone call and arrange the hit.
The published book was a rewrite and would not have the secret message in the chapter beginnings.
The published book was a rewrite of the original manuscript. He gives her the original manuscript that he was working off, not a final draft.
We know the beginning of the book was rewritten as he didn't like it. Almost certainly, the clue is not in the published version of the book. Ruth was shocked to read the note and is delivering her speech so is unlikely to be complicit in the murder of the Ghostwriter. The ending suggests that Ruth, too, is little more than a pawn in the whole conspiracy.
Makes no sense, he was run down 2 minutes after she read it.