There are the following functions for working with documents:
doc_create - Create a document, with or without an ID
doc_update - Update a document
doc_get - Get a document
doc_delete - Delete a document
doc_head - Get headers for a document
doc_attach_create - Attach something to a document
doc_attach_info - Get info on an attachment
doc_attach_get - Fetch an attachment
doc_attach_delete - Delete an attachment
db_alldocs - Get all documents
db_revisions - Get revisions for a document