If using the file-browser within the Pages App (per your screenshot - it says “Pages” at the top of the left-hand browser pane), any files that are “greyed-out” are not compatible with - and cannot be opened by - the Pages App. Only files that Pages can open are not ghosted.
If instead you open the native Files App on your iPad (at the top of the left-hand browser pane it will say “Browse”) and navigate to the same location/path in your filesystem - all files in this path will be accessible; the PDF files will not be greyed-out - and can be opened by your iPad using its native PDF reader.
The “subtle” differences between the file-browser of Pages (also applies to the Keynote and Numbers productivity Apps) and the full Files App often catch-out the unwary.
If you wish, you can also install one of the dedicated PDF Apps that are available within the Apple App Store - one of the best known and recognisable being Adobe Reader (which is also essentially free). This will provide an alternative App with which to open PDF files.
Does this answer your question and solve the problem?