On the occasion of the 400th anniversary of the Sikh Holy Book, Guru Granth Sahib, the Times of India has an article about the history of it.
The master copy of the Adi Granth was initially kept by Guru Hargobind in his house. From there it was stolen by his grandson Dhir Mal who intended to use it to further his claims on succession. Some 30 years later, followers of the Guru Teg Bahadur forcibly recovered it, but were instructed by the guru to return it. The holy book emerged from obscurity only in 1849. [Descendants of Arjan Dev have original text]
The Adi Granth, written by Guru Arjan Dev, is the original scripture, also known as Kartarpuri Bir, and was installed at the Golden Temple on September 1, 1604. The genuineness of this master copy, scripted by Bhai Gurdas under the direct supervision of Guru Arjan Dev, had been vouched by top Sikh scholars, including Bhai Jodh Singh, after thorough scrutiny of the holy text, which bears the original signatures of Guru Arjan Dev.