?????? PDF does not display font

for a while now, each time I open a particular PDF it will only display "?????" where the fonts are supposed to be.

how do I correct this problem.
I have no way of finding which font I am missing

any help you can provide will be much appreciated

You might have a corrupt font. Do you have the file the pdf was made from? If so, change the font there and make a new pdf.

Open a .pdf with what? I've tried a .pdf file with Adobe Pro, and for the life of me I can't see anything to with Fonts.

If I create a new .pdf file with Pro however, I see the font window - but only the one font available, Arial. I cannot change it, and I cannot change its size.

I open said .pdf file again, but with Adobe Reader. No font facility available (it is, after all, just a reader). Same with Preview incidentally.

Is your particular .pdf file coming from a Win computer with non-Mac fonts, or, do you not have Arial font installed on your Mac?