Eric’s suggestion in the referenced post does apply to your general issue. (Others using Keynote have raised similar questions.)
The important point is that PowerPoint and Keynote files are not among the file types that DT is designed for. See the discussion on PowerPoint files under Requests & Suggestions.
Especially important is the fact that Keynote files are package files. When DT imports package files, it treats them as folders rather than packages. For many types of documents that are saved as packages, that can cause real problems.
I don’t have Keynote and haven’t experimented with that app’s files. But I do have several apps that save documents as packages, including Create, NoteTaker and CP NoteBook. Neither directly linking to, nor importing (for example, a NoteTaker or NoteBook document) gives useful results, and attempting to store a CP NoteBook file in DT and then export it results in a file that cannot be opened in the NoteBook app (that’s not good).
So to be on the safe side, I don’t import such file types.
But I often do want to add the text contained in some “foreign” file type documents to my DT database, and to be able to open the original easily from DT.
I believe Keynote (as does PowerPoint) allows one to export the presentation’s text as an RTF file. Do that, and import the RTF file into DT. Then open the new import’s Info pane and paste the URL path or the UNIX path of the presentation file into the Path field of the Info pane. Now you’ve got the searchable text of the presentation in DT, and you can quickly find and open the original Keynote file.
I’ve got a number of useful PowerPoint presentations on technical subjects, and have integrated them into my DT database in this way.
Or, as Eric suggested, print the PowerPoint or Keynote file as a PDF, then import the PDF into DT. (If you wish, you can use the ‘trick’ described above to substitute the PDF file’s Info path with the URL path or UNIX path of the original presentation file, so that it can be directly opened with a click.)
Comment: My approach of exporting the text of a presentation file rather than doing a print to PDF takes a lot less disk storage space, which is why I favor it. Doing this takes a couple of minutes per presentation file.
Comment 2: I prefer not to import foreign files into my database Files folder. Instead, I keep them in their original locations on my drive, and use path links so that I can search and view their text in DT, and open them under their native app via a click on the Info pane path link. That way, I don’t have to worry about how DT treats package files, or the possible corruption of package documents.