1 import S1 SLC data into SNAP
Data > Import > SAR Sensors > Sentinel-1
2 Apply TOPS Split
reduce the number of bursts as much as possible
3 Radiometric Calibration
select complex output
4 TOPS Deburst
5 Multi-Looking
optional, I only applied it to reduce the resolution (sometimes introduces stripes)
6 Compute polarimetric parameters or decompositions
Radar > Polarimetric > Decomposition / Classification
7 Results
As you see, the quality is not so great, because these tools require HH and HV as well. But technically you can compute many of the things and I don’t think that PolSARpro will lead to different or better results.