Basically, two types of .easm files from SolidWorks exist. First type that is exported just to be used for viewing, measuring and commenting purposes and you cannot convert it back to the original data.
The other type was saved with the "allow save" function enabled, which means they can be exported as STL files for Stereolithography (3D printing). These .easm files can be used to get your .sldprt files back, but it can probably be done only in Solidworks and no 3rd party app may help you here.
With 3rd party programs you would have to convert STL to some generic CAD part format and convert that back to SLDPRT with a program that supports both of these formats.
Updated: September 28, 2016