This is a bit of a mischaracterization of secure hashing.
You can not uniquely reconstruct a document from a hash value. Indeed, for a typical secure hash function, a given hash value maps to an infinite set of inputs. But because secure hashes are one-way functions, finding any of those inputs for a given output requires brute force. This is why the bidding example works - it's so hard to find any input that hashes to a value that even having one of them is reasonable proof that it was the source document.
*Consider a secure 1024-bit hash function. How many 1025-bit inputs map, on average, to each hash value?