  The observed diversity of exoplanets can possibly be traced back to the
planet formation processes. Planet-disk interactions induce sub-structures in
the circumstellar disk that can be revealed via scattered light observations.
However, a high-contrast imaging technique such as polarimetric differential
imaging (PDI) must first be applied to suppress the stellar diffraction halo.
In this work we present the PDI PiPelIne for NACO data (PIPPIN), which reduces
the archival polarimetric observations made with the NACO instrument at the
Very Large Telescope. Prior to this work, such a comprehensive pipeline to
reduce polarimetric NACO data did not exist. We identify a total of 243
datasets of 57 potentially young stellar objects observed before NACO's
decommissioning. The PIPPIN pipeline applies various levels of instrumental
polarisation correction and is capable of reducing multiple observing setups,
including half-wave plate or de-rotator usage and wire-grid observations. A
novel template-matching method is applied to assess the detection significance
of polarised signals in the reduced data. In 22 of the 57 observed targets, we
detect polarised light resulting from a scattering of circumstellar dust. The
detections exhibit a collection of known sub-structures, including rings, gaps,
spirals, shadows, and in- or outflows of material. Since NACO was equipped with
a near-infrared wavefront sensor, it made unique polarimetric observations of a
number of embedded protostars. This is the first time detections of the Class I
objects Elia 2-21 and YLW 16A have been published. Alongside the outlined
PIPPIN pipeline, we publish an archive of the reduced data products, thereby
improving the accessibility of these data for future studies.
