Converting eDrawings (.easm) files back to original Solidworks parts (.prt) will be possible only if the original creator and the one that exported to eDrawings in the first place did select that option in export settings. Except for that, it seems that successful easm to prt conversion is really hard to achieve as the purpose of .easm fies is primarly for viewing or publishing without the option to further alter these file.
Open EASM file Open PRT file