An ACSM - Adobe content Server Message file enables a person to manage and read ebooks and other digital publications. It contains the data needed to download an ebook but is not the ebook in itself.
This particular file type is used by Adobe Digital Editions and Adobe Content Server. A person who wants to open the program can do so with Digital Editions.
Most people who attempt to legally download an ebook will get an ACSM - Adobe content Server Message file even if they do not use an Abobe based eReader program. However, a person will need to download Adobe Digital Editions in order to download the ebook using this file type. After the ebook has been downloaded, a person can read the ebook using the eReader program of his or her choice.