Yes, if the database ACL you are accessing does not have default reader or anonymous access you can pass the username / password to authenticate with the database.
The DominoPDF method would be as below;
WebUsername=value – If the URL connection requires authorisation the HTTP username can be specified. (Note this is the username for web access not Notes access).
WebPassword=value – If the URL connection requires authorisation the HTTP password can be specified. (Note this is the password for web access not Notes access).
If the URL connection requires proxy authorisation the HTTP proxy username and password can be specified.
WebProxyUsername= – If the URL connection requires proxy authorisation the HTTP proxy username can be specified. (Note this is the username for web access not Notes access).
WebProxyPassword= – If the URL connection requires authorisation the HTTP proxy password can be specified. (Note this is the password for web access not Notes access).