fonts changing to symbols

[deving40067335]

I can create multiple pdfs from autocad 2017 that look perfect alone.  When I combine them using Acrobat 2017 it'll change the 'Notes' from a standard arial font to symbols and characters.  Any help is appreciated.  Windows 8.1 -  

My first action was to reinstall acrobat...nothing changed.  Next, I went back through all my AutoCad layouts and switched any and all fonts to Arial.  This proved to work for a little while but now we are back in the same situation.

I recently sent my individual pdfs to a fellow architect and he was able to combine them without a hitch.  He is on windows 10.

Even when I was combining and not having problems I had a customer with a Mac system that could not read the font.  That is what lead me to switch all font's to a universal standard Arial.  I have figured out a work around for now.  When I combine them even tho the text is symbols I can then print to PDF and it will lock in the original fonts.  Not that big of issue just another step

Are my files somehow being encrypted??? 

thanks in Advance

[Karl Heinz Kremer · Accepted solution]

No, your files are not encrypted. You are very likely dealing with a problem caused by subset embedded fonts, where the different subsets share the same name, so Acrobat assumes that it is dealign with the same font and that ends up corrupting the data in some of your files that you combine. Take a look here for a potential workaround: Workaround for Missing Characters After Merging PDF Files​