  In the third paper of this series we continue the exploitation of Kepler/K2
data in dense stellar fields using our PSF-based method. This work is focused
on a ~720-arcmin^2 region centred on the Solar-metallicity and Solar-age open
cluster M 67. We extracted light curves for all detectable sources in the
Kepler channels 13 and 14, adopting our technique based on the usage of a
high-angular-resolution input catalogue and target-neighbour subtraction. We
detrended light curves for systematic errors, and searched for variables and
exoplanets using several tools. We found 451 variables, of which 299 are new
detection. Three planetary candidates were detected by our pipeline in this
field. Raw and detrended light curves, catalogues, and K2 stacked images used
in this work will be released to the community.
