Why does this PDF prompt 'anydoc. Unsupported Error: unsupported input: PDF has no extractable text (ImageBased, 1 pages)'

Why does this PDF prompt 'anydoc. Unsupported Error: unsupported input: PDF has no extractable text (ImageBased, 1 pages)'? Is this the expected result？ The PDF file can be found at the following link, and the code is shown below

[document_with_images.pdf](https://github.com/user-attachments/files/31766562/document_with_images.pdf)

```python
import anydoc

markdown = anydoc.to_markdown("document_with_images.pdf", ocr="hosted")
with open("anydoc_result.txt", "w", encoding="utf-8") as f:
f.write(markdown)
print("written to anydoc_result.txt")
```

Reproduce the report with document_with_images.pdf using anydoc.to_markdown("document_with_images.pdf", ocr="hosted"). Start by tracing PDF classification and OCR routing for an image-only, one-page PDF. Done means establishing whether the unsupported-input result is expected and documenting or correcting the observed behavior.

Written by the indexing model from the issue text.