Here are some impressions that I had when creating the same service as you (reading and saving a PDF file on a network drive). I had 2 drives: the first without authentication, and the second for authentication.
Common errors with mapped network drives
UNC- : , , UNC. (,\\10.17.194.1\RemoteDir \)
: , , , , . "RemoteUser" "RemotePassword", RemoteUser/RemotePassword .
, , , / , , .
: , , . , ββ .
, .