Christiane Feldmann-Leben wrote:
If the programme doesn't recognize the document, then maybe you have a pdf-format which doesn't allow OCR, which some clients send without knowing what trouble they cause. Then no programme will help.
Not really. There are programs that remove protections from PDFs, just search in Google.
The only way I know (if the client isn't willing to send another pdf-format), to print everything out and scan it manually. Then OCR is possible again.
Alternatively, you can try printing your PDF out to a new PDF using programs such as pdfcreator.