As FF2 says, the .acsm file is a "ticket" to get the actual .epub file from Adobe's (or OverDrive's) servers. So, first you should open it with Adobe Digital Editions (don't forget to register 1st for an AdobeID). This should all be explained on your library's web site.
Once you can read the ePub in ADE, then you can import the .epub file into Calibre and strip the DRM during the import using a 3rd party plugin. Since you already have the required "inept" plugin, read its README and follow instructions.
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