Sometimes it happens to users when they are trying to open an attachment, say a PDF from a document. There is no code here.
E.g. Http Worker Thread ID [e14]: Working session [3fb]: Session State [Processing Request] : Client IP Address [10.18.9.182] : User Name [Anonymous] : GET /report/report.nsf/0/0DA6A7B9159F8AE788257FAE0046BDF4/$File/Labeling%20Requirements.pdf?OpenElement HTTP/1.0