Is Paprocki a common surname among Poles?
No, I don't think it's a common surname.
Most popular surnames are: Nowak, Kowalski and many others. Here is a list of the most popular Polish surnames :
220217 Nowak
131940 Kowalski
104418 Wiśniewski
92945 Dąbrowski
89366 Lewandowski
88932 Wójcik
87935 Kamiński
87690 Kowalczyk
85988 Zieliński
84527 Szymański
81390 Woźniak
72368 Kozłowski
65942 Jankowski
63519 Wojciechowski
62629 Kwiatkowski
59403 Kaczmarek
futrega.org/etc/nazwiska.html