Problem with local (non-english) text

whereas sumatraPDF will show correctly Greek PDFs and other “exotic” languages, when you select and copy out text it doesn’t agree with the text shown e.g. ΙΔΙΟΚΤΗΤΗΣ will turn to IATOKTHEIA or something.

This affects both the viewer and the text filter (IFilter) meaning that windows search index won’t work properly either for non-English text

is there anything that can be done?

Maybe but also maybe not. It depends on the document.

In PDF files, you can embed subset of fonts and when not done correctly, this mapping loses the link between the glyph index (the index of character in the font file) and the actual character.
If other PDF viewers do it better, then it’s a bug in Sumatra. If not, then it’s a bug in PDF file.

you are right, it must be a problem with the particular PDF. I created a test PDF myself and Sumatra copied the text correctly!