Known problems

Here I copy a reply to one user who reported this problem to make it available to others:

I have had a look at the problem you reported. As I was afraid, it is a
problem caused by different handling of fonts in Tkinter (the library
that BKChem uses to display windows) and Cairo (the library used for PDF
export). These two libraries have separate ways of finding fonts and it
sometimes happens that they find a different one for the same name or
that Cairo cannot find that font at all and uses some replacement. It
can then happen that the font looks slightly different or that some
non-ASCII letters disappear or a replaced by some other strange symbol.
I am sorry but there is not much I can do about it. The only way is to
try to change the font (I was successful with Arial) and re-try the export.