In each proposals of the DAO there is a hash that I guess is here for us to check the proposal document matches the submission. But where to find these documents? Any official link where links to each proposal are listed? How can we vote if we can't read the original paper? Thanks.
No, it's not that the meaning.
Proposal hash is actually formed by recipent, amount and transaction data:
proposalHash = sha3(_recipient, _amount, _transactionData);
recipient: The recipient of the transaction. This is an address, which can only be the address of the DAO itself, the Curator or an address on the whitelist allowedRecipients. Any other address will throw an exception, blocking you from creating a new proposal. The whitelist is curated by the Curator, and only they can add/remove addresses to/from that list. There is an exception to this rule. When making a proposal for a new Curator, the recipient is the address of the proposed Curator (typically a multisignature account of trusted people, or in the case a user is splitting to form their own personal DAO, their own account address).
amount: The amount of wei (1 = 10^-18 ether) to be sent from the DAO to the recipient in the proposed transaction.
transactionData: The data of the proposed transaction. This is used to call functions in the case the recipient is a smart contract, and optionally to provide the function parameters of this smart contract to the DAO itself.
See more about how to create proposal at the official GitHub Wiki Page