docs: document auto model selection and document file attachments (v1.0.32)

- Chapter 01: Add note about 'auto' model option that lets Copilot
  automatically pick the best available model for each session
- Chapter 02: Add document file (.pdf, etc.) support to the @ patterns
  table and 'Working with Images' section, now titled 'Working with
  Images and Documents'

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: DanWahlin

01-setup-and-first-steps/README.md

@@ -484,6 +484,8 @@ copilot
 # Shows available models and lets you pick one. Select Sonnet 4.5.
 ```
 
+> 💡 **Not sure which model to pick?** Select **`auto`** from the model list to let Copilot automatically choose the best available model for each session. This is a great option when you're just getting started and don't want to worry about model selection.
+
 > 💡 **Tip**: Some models cost more "premium requests" than others. Models marked **1x** (like Claude Sonnet 4.5) are a great default. They're capable and efficient. Higher-multiplier models use your premium request quota faster, so save those for when you really need them.
 
 </details>

02-context-conversations/README.md

@@ -75,6 +75,9 @@ copilot
 | `@file.py` | Reference a single file | `Review @samples/book-app-project/books.py` |
 | `@folder/` | Reference all files in a directory | `Review @samples/book-app-project/` |
 | `@file1.py @file2.py` | Reference multiple files | `Compare @samples/book-app-project/book_app.py @samples/book-app-project/books.py` |
+| `@document.pdf` | Reference a document file | `Summarize @requirements.pdf` |
+
+> 💡 **Document files**: In addition to code files and images, you can attach supported document files (such as PDFs) to your prompts using the same `@` syntax. This lets the agent read and reason about specs, requirements, or any document alongside your code.
 
 ### Reference a Single File
 
@@ -673,7 +676,7 @@ This staged approach keeps context focused and efficient.
 <summary><strong>Working with Images</strong></summary>
 <a id="working-with-images"></a>
 
-### Working with Images
+### Working with Images and Documents
 
 You can include images in your conversations using the `@` syntax, or simply **paste from your clipboard** (Cmd+V / Ctrl+V). Copilot CLI can analyze screenshots, mockups, and diagrams to help with UI debugging, design implementation, and error analysis.
 
@@ -685,6 +688,14 @@ copilot
 > @images/mockup.png Write the HTML and CSS to match this design. Place it in a new file called index.html and put the CSS in styles.css.
 ```
 
+You can also attach **document files** (such as PDFs) to provide requirements, specs, or any written reference material:
+
+```bash
+copilot
+
+> @requirements.pdf Implement the feature described in this document for @samples/book-app-project/book_app.py
+```
+
 > 📖 **Learn more**: See [Additional Context Features](../appendices/additional-context.md#working-with-images) for supported formats, practical use cases, and tips for combining images with code.
 
 </details>