I am not sure if there is a document that says ASA comes with ASDM but I think its a given fact that there is always some version of the ASDM software of the ASA Flash memory when its shipped. If not I would imagine it would be a used device.
To download ASA software and ASDM software you need a service contract that is attached to the account at cisco.com.
As noted already, every ASA sold through authorized channels will ship with ASA and ASDM binaries already included on the internal compact flash (disk0).
It is only necessary to download an new file from cisco.com if you wish to upgrade your ASDM (or if you inadvertently erase yours or it is destroyed due to hardware failure).
A download requires a service contract unless the loss was covered under the initial warranty. The other exception I can think of is when Cisco issues a security advisory (PSIRT) specific to the product. In those cases they sometimes make free downloads available if you are an affected customer.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...