  Narrow-line Seyfert 1 (NLS1) galaxies are a class of active galactic nuclei
(AGN) that, in some cases, can harbor powerful relativistic jets. One of them,
PKS 2004-447, shows gamma-ray emission, and underwent its first recorded
multifrequency flare in 2019. However, past studies revealed that in radio this
source can be classified as a compact steep-spectrum source (CSS), suggesting
that, unlike other gamma-ray sources, the relativistic jets of PKS 2004-447
have a large inclination with respect to the line of sight. We present here a
set of spectroscopic observations of this object, aimed at carefully measuring
its black hole mass and Eddington ratio, determining the properties of its
emission lines, and characterizing its long term variability. We find that the
black hole mass is $(1.5\pm0.2)\times10^7$ M$_\odot$, and the Eddington ratio
is 0.08. Both values are within the typical range of NLS1s. The spectra also
suggest that the 2019 flare was caused mainly by the relativistic jet, while
the accretion disk played a minor role during the event. In conclusion, we
confirm that PKS 2004-447 is one of the rare examples of gamma-ray emitting
CSS/NLS1s hybrid, and that these two classes of objects are likely connected in
the framework of AGN evolution.
