some original letters disappear when i try to edit

Hi kristenz84392186 ,

Please provide the exact dot version of the software & OS installed at your system .Also check whether is there any update available for the software after going through "help > check for updates "

Follow this thread to reset the preferences for the Acrobat software  :- How to reset Preference settings in Acrobat.

Please try to export the Document to '.tiff' format , then again open that document in Acrobat Again & try to edit it.

If the same issue persist then check with the other documents.
Also the name of the application using which the document is originally created.

Regards,

Yatharth