Update documentation for file detail view features

- Added comprehensive documentation in User Guide for new file detail features
- Updated API documentation with reprocess and preview endpoints
- Documented retry button functionality and use cases
- Documented process flow visualization feature
- Documented file preview feature with examples

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

docs/API.md

@@ -91,16 +91,49 @@ Retrieve metadata for a specific file.
 
 **POST** `/api/files/{file_id}/reprocess`
 
-Reprocess a specific file.
+Reprocess a specific file. This queues the file for complete reprocessing through the entire pipeline.
 
 **Response**:
 ```json
 {
-  "success": true,
-  "message": "File queued for reprocessing"
+  "status": "success",
+  "message": "File queued for reprocessing",
+  "file_id": 123,
+  "filename": "invoice.pdf",
+  "task_id": "a1b2c3d4-e5f6-7g8h-9i0j-k1l2m3n4o5p6"
 }
 ```
 
+**Error Responses**:
+- `404`: File not found
+- `400`: Local file not found on disk (cannot reprocess)
+
+### File Preview
+
+**GET** `/api/files/{file_id}/preview`
+
+Retrieve the file content for preview purposes.
+
+**Parameters**:
+- `version` (required): Either `original` or `processed`
+  - `original`: Returns the file as it was uploaded (from tmp directory)
+  - `processed`: Returns the file after metadata embedding (from processed directory)
+
+**Response**: Returns the file content with appropriate MIME type for browser display.
+
+**Example**:
+```bash
+# Preview original file
+curl "http://<your-instance>/api/files/123/preview?version=original"
+
+# Preview processed file
+curl "http://<your-instance>/api/files/123/preview?version=processed"
+```
+
+**Error Responses**:
+- `404`: File not found in database or on disk
+- `400`: Invalid version parameter
+
 ### Batch Processing
 
 **POST** `/api/processall`

docs/UserGuide.md

@@ -69,6 +69,51 @@ The **Files** page provides access to all processed documents:
 3. Click on any file to view its details
 4. Sort the list by any column by clicking on the column header
 
+### File Detail View
+
+When you click on a file, you'll see a comprehensive detail view with the following sections:
+
+#### File Information
+This section displays metadata about the file:
+- File ID and original filename
+- File hash (SHA-256)
+- File size and MIME type
+- Creation timestamp
+- Local path and disk status
+
+#### Processing History
+View the complete processing history with a timeline showing:
+- Each processing step that was executed
+- Status of each step (success, failure, in progress, pending)
+- Error messages for failed steps
+- Timestamps for each operation
+
+**Retry Processing**: If a file's processing has failed, you can use the "Retry Processing" button to reprocess the entire file. This is useful when:
+- External API services (like OpenAI) had temporary issues
+- Network connectivity was lost during processing
+- Configuration has been updated and you want to reprocess with new settings
+
+#### Process Flow Visualization
+The process flow visualization shows a visual representation of the document processing pipeline:
+- **Green indicators**: Successful stages
+- **Red indicators**: Failed stages with error messages
+- **Gray indicators**: Stages that were not executed (e.g., because a previous stage failed)
+
+This helps you understand:
+- Which processing path your document took (local text extraction vs. OCR)
+- Where exactly the processing failed
+- Which stages were skipped and why
+
+#### File Previews
+If your file is still available on disk, you can preview it directly in the browser:
+- **Original File**: The file as it was uploaded
+- **Processed File**: The file after metadata has been embedded (if processing completed)
+
+Both previews support:
+- In-browser PDF viewing
+- Opening in a new tab for full-screen viewing
+- Side-by-side comparison of original and processed versions
+
 ## Document Processing Features
 
 Depending on the system configuration, DocuElevate can perform: