Thank you @Philip Lees, I will try.
Philip Lees wrote:
It isn't clear to me how you converted the file and Windows obviously has no idea what's wrong with it.
Suggestions:
1. Try converting the PDF to a different Word-readable format, e.g. .doc instead of .docx, or .rtf, or .odt.
2. Try using different software to convert the file. There are free on-line PDF to Word converters, some with limitations. I use ABBYY Fine reader, which is usually pretty good.