Well, this was new to me, so I had to look it up. There is a good introduction to PNG files, for those (like me) who need it. I also found a good FAQ about PNG.
Basically PNG is an alternative image format for Web pages, like GIF or TIFF. It sounds like your question is whether the Notes client software will correctly display a PNG image from a Notes document. The answer appears to be "no." Here is a quote fromj someone who should know on Notes.net.
RE: Importing a file using LotusScript (PNG)
Posted by Stan Rogers on 28.Oct.02
No, Notes doesn't speak PNG. You can attach it or paste it as pixels, or convert to JPEG/GIF/TIFF/BMP before importing, but you can't import a PNG directly.
This was first published in May 2003