It is not possible to share a document from within Google Documents and have it BCC all the recipients. This is a feature that has been requested a lot over the past several years on the Google product forums (e.g. here, here, here, and here), and so far Google has not implemented it.
I saw a couple people in those threads mention a workaround that will only work if you want to share a document to people with "can view" access. In that case, you share the document with "Can view" access to everyone but do not select the "Notify people via email" box. Then you take the link to the document and send it in a regular email to everyone in the Bcc line.
That workaround will not work if you want to share a document to people with "can edit" access. This is because anyone with edit access can click on the document's "Share" button and see all the other editors' email addresses.