I have a mobile service bill (from Verizon) imported from my account (i.e., not scanned locally). Although the text can be selected when displayed within DT3, the file type is shown as PDF Document; contents do not show up in a search; the concordance is blank.
The text layer is accessible in PDFPen Pro and Preview; Within DT3 I can select and copy text, and paste into a DT3 note, so the text is available for some purposes but not all.
Document PDF version is 1.4
The document producer is "Ricoh Americas Corporation, AFP2PDF Plus Version: 1.200.11
Also, if I re-OCR within DT3, the file size goes from 260.4 KB to 2.4 MB.
DT3.5.1, Mojave 10.14.6.