I had an import problem which I eventually resolved simply by renaming the file I wanted to import. The file was RTF. It had been named: 3. Gelpi Yong General Introduction 1[1].1PDM
Under that name all that imported was the shortened filename "3 " but no text. I gave it a new one word filename and it imported correctly.
I see from “Known bugs” reports that a (?) double full stop stops import, and there is also a known bugs item regarding invalid filename characters.
Would it be worth combining these reports and signalling under the heading Import that files will fail to import if filenames include certain characters?