I am trying to open an old *.ppt in Libre Impress, but from slide 20 onward the text is all converted to symbol font and its all greek characters. I tried to change it to a different font but it ends up just as rectangles. Anybody know how to fix this problem or at least recover the text that was there?? (The ppt had been made in MS powerpoint originally)
The old PPT format is a binary one, so try to determine what is wrong with these files requires an expert. At the very least you will need to upload a copy of the file somewhere and edit your question to provide a link, so that others can examine the file. It could be anything from a font-related issue to file corruption that you are seeing.