I have imported two pdfs in my DTPO (1.3b2) database.
Although the pdfs are in the database and I can read them properly, the Import protocol, which always appears, when there are problems with importing, says: no text.
[1] The PDF is image-only, and contains no text. OCR could convert the original PDF to PDF+text if the resolution of the original PDF is sufficiently high (150 dpi, or (better) 300 dpi or higher).
[2] The original PDF is encrypted, so that DT isn’t allowed to read and capture the text.
You can open the original PDF in Preview to check it.
If you can’t search for any word at all in Preview, the PDF is image-only.
If you can search successfully for a word in Preview, the PDF contains text. Now see if you can select and capture to the clipboard some text from the PDF. If you cannot, the PDF is probably copy-protected. (There are third-party utilities that can ‘break’ normal copy protection.)