A text-based PDF contains character objects that a reader can select, search, and copy. It may have been exported from Word, a browser, publishing software, or another application. A scanned PDF usually contains page-sized images instead, even when the page visibly contains words.
This converter does not perform OCR. PDFMK checks every page in your browser and reports how many contain selectable text before the file is uploaded. Mixed documents are supported when at least one selected page contains text, but image-only pages remain image content rather than becoming newly recognized text.
Unsure what you have? Read Scanned vs. Searchable PDFs for selection, search, and zoom tests.