no differences but two completely different pdf.How to solve it?

[ushio20]

no word list
no word list
Traceback (most recent call last):
File "/opt/conda/bin/pdf-diff", line 8, in
sys.exit(main())
File "/opt/conda/lib/python3.6/site-packages/pdf_diff/command_line.py", line 498, in main
img = render_changes(changes, style, args.result_width)
File "/opt/conda/lib/python3.6/site-packages/pdf_diff/command_line.py", line 193, in render_changes
raise Exception("There are no text differences.")
Exception: There are no text differences.