An ACSM file is generated when you download an ebook from ProQuest eBook Central. ACSM stands for Adobe Content Server Message and is not the ebook you want to download. Instead, the ACSM file is a message that says "download this book, please". To fulfil the "download this book, please" request, you need the free app Adobe Digital Editions and an Internet connection. When you open the ACSM file, the ebook will be downloaded onto your device.
Why is this necessary? Publishers restrict access and availability to their titles though digital rights management (DRM) which prevents the unauthorised copying or redistribution of eBooks in order to protect the rights of authors and publishers. The DRM is enforced through Adobe Digital Editions and .acsm files
See also:
ProQuest eBook Central: Downloading
What is digital rights management (DRM)?
