Use the save verb when an actor is saving an object. Since this is a fairly trivial or common activity the distribution of this may be limited to the user's lifestream or a smaller audience than post or share. For more information see: http://martin.atkins.me.uk/specs/activitystreams/activityschema#save
http://activitystrea.ms/schema/1.0/save
Any object that can be posted can be saved. Also target can be used to convey the album or folder where the content was saved to.
Matt saved a file "http:\\files.com\Q1 Metrics.xslx"