  The Probability Density Function (PDF) provides an estimate of the
photometric redshift (zphot) prediction error. It is crucial for current and
future sky surveys, characterized by strict requirements on the zphot
precision, reliability and completeness. The present work stands on the
assumption that properly defined rejection criteria, capable of identifying and
rejecting potential outliers, can increase the precision of zphot estimates and
of their cumulative PDF, without sacrificing much in terms of completeness of
the sample. We provide a way to assess rejection through proper cuts on the
shape descriptors of a PDF, such as the width and the height of the maximum
PDF's peak. In this work we tested these rejection criteria to galaxies with
photometry extracted from the Kilo Degree Survey (KiDS) ESO Data Release 4,
proving that such approach could lead to significant improvements to the zphot
quality: e.g., for the clipped sample showing the best trade-off between
precision and completeness, we achieve a reduction in outliers fraction of
$\simeq 75\%$ and an improvement of $\simeq 6\%$ for NMAD, with respect to the
original data set, preserving the $\simeq 93\%$ of its content.
