  PG1535+547 is a bright NLS1 galaxy, whose high energy emission shows strong
variability in shape and flux. ROSAT data classified it as soft X-ray weak QSO
(objects whose X-ray-to-optical flux ratio is smaller than in typical QSO):
their X-ray spectra are often characterized by highly ionized, complex
absorbers and/or reflection from the disk, whose relative importance is
currently debated. In both cases, the presence of such features implies that we
are looking at matter located in the innermost regions of the AGN. In this
paper we want to clarify the nature of the X-ray emission of PG1535+547, and
constrain the physical properties of regions where the emission originates. We
present new XMM observations, from which we obtained 2 spectra separated by
about 1 week, that we compare with a previous XMM observation. The data support
the complex and variable nature of the X-ray emission. The broad band flux
increases by a factor ~2.3 in 3 years, and then decreases by a factor ~1.3 in
about 1 week. In the new EPIC spectra strong absorption features at E<3keV and
a complex spectral shape in the Fe line energy range are evident, coupled with
a drop in the emission at higher energies. We describe all the states assuming
either a warm absorber plus a relativistically blurred ionized reflection, or a
two-phase warm absorber partially covering the source plus a scattered
component. The variability is ascribed to the warm absorbers, that vary their
physical properties on timescales of years and days. In the reflection scenario
all the states require a high fraction of reflection. The strong variability in
the X-ray band opposed to a more constant optical emission implies that
PG1535+547 can not actually be classified as a soft X-ray weak AGN.
