C# API PDF Downloader

I need a straightforward C# utility that connects to a REST-style endpoint on a third-party website, pulls down PDF files, and saves them locally. I will supply the endpoint URL, any required headers or tokens, and several sample document IDs once the project starts.

Core expectations
• Use modern .NET (6 or later preferred) with HttpClient or RestSharp for the calls.
• Accept one or many document IDs from the command line or a small config file, request each PDF, and store it with a sensible filename in a chosen folder.
• Log basic progress and any non-200 responses so I can troubleshoot failed downloads easily.
• Code should be clean, commented, and buildable with a single dotnet build command.

Deliverables
1. Full source (csproj, Program.cs, helper classes).
2. A short README explaining any third-party packages and how to run the tool.
3. A compiled executable for quick testing.

This is a focused task; once the first PDF downloads successfully and the code is tidy, we’re done.