docs(bf-4axmo): verify JavaScript PDF test fixture

Located and verified js_in_openaction.pdf fixture:
- Path: tests/document_model/fixtures/js_in_openaction.pdf
- Size: 632 bytes, PDF version 1.4
- Currently malformed (missing /Root reference)
- Documented fixture properties and expected behavior

Closes bf-4axmo

notes/bf-4axmo.md

@@ -0,0 +1,48 @@
+# JavaScript PDF Test Fixture Verification (bf-4axmo)
+
+## Summary
+
+Located and verified the JavaScript PDF test fixture exists and is accessible.
+
+## Fixture Details
+
+**File:** `js_in_openaction.pdf`
+**Path:** `/home/coding/pdftract/tests/document_model/fixtures/js_in_openaction.pdf`
+**Size:** 632 bytes
+**Permissions:** `-rw-r--r--` (0644)
+**Last Modified:** 2026-07-05 19:51:55
+**PDF Version:** 1.4
+
+## File Verification
+
+✅ **File exists:** Confirmed via `ls -la` and `stat`
+✅ **File is readable:** Standard permissions (0644) allow read access
+✅ **PDF header valid:** File starts with `%PDF-1.4` signature
+✅ **File accessible:** Full path `/home/coding/pdftract/tests/document_model/fixtures/js_in_openaction.pdf`
+
+## Current Expected Behavior
+
+According to `js_in_openaction.expected.json`, this fixture currently produces:
+- `contains_javascript: false` (due to parsing error)
+- Error: "Failed to parse PDF: No /Root reference in trailer"
+- Page count: 0
+
+## Notes
+
+The fixture name (`js_in_openaction`) suggests it should contain JavaScript in the PDF's OpenAction dictionary, but the current expected output indicates a malformed PDF (missing /Root reference in trailer). This may be intentional for error handling testing.
+
+## Other Fixtures
+
+Total of 14 PDF fixtures in the main fixtures directory:
+- `base_hello.pdf` (no .expected.json)
+- 4 encryption test PDFs
+- 9 structural/conformance test PDFs
+- 1 JavaScript-related PDF (`js_in_openaction.pdf`)
+
+## Status
+
+All acceptance criteria met:
+- ✅ JavaScript PDF fixture file path identified
+- ✅ File exists and is readable
+- ✅ File size and basic properties noted
+- ✅ File location documented for next step