The type of font encoding used has to match. Acrobat does not use fonts in the same way as a word processor. However, the simplest way to make this change and retain your layout and such is to make the change in your WORD document and create a new PDF. Trying to make such changes in the PDF is not an efficient workflow process.
No, Acrobat is not a word processor.
More to the point Acrobat lets one "work" PDF and PDF is not a file format designed as a word processing, editing, formating, or page layout file format.
PDF is, essentially, a "final destination" format.
What it is is described in the ISO Standard for PDF (ISO 32000-1).