Cannot change font, size or anything for typewriter tool

Hello all,

I am having an issue with the typewriter tool.  I cannot seem to change my font on about 95% of my PDFs?  Every once in awhile I am able to change the font and size.  But I cannot find a consistancy and cannot figure out the issue?  When I want to write on the PDFs to change size or font, it won't allow me to.  Any ideas?

Thanks,

Lorne