Georgian language in InDesign

The font in that PDF must not be Unicode compatible; or, the font embedding does not contain proper translations from its local encoding into the Unicode encoding that InDesign expects from all well-behaving fonts.

Check what font name is reported in Acrobat, and see if you can install and apply that. Although, even if that works, you should consider not using it – your documents, in turn, would not be properly Unicode compatible as well.

I would bite the bullet and replace each badly encoded character in turn with the proper Unicode character. You would only have to do this once. See also this very similar InDesignSecrets question: https://indesignsecrets.com/topic/ewe-characters-shown-as-a-red-box

Unrelated to your encoding problem: InDesign should not be having any problem at all typesetting (properly encoded ) Georgian text. You may have to acquire a specialty font, though. My modern Windows machine only supports Georgian in Arial Unicode and Segoe UI – and the latter only because it's a Windows 10 font designed specifically for UI support. Off-hand, I'd guess the situation on a Mac won't be much better.

Looking up some Georgian characters on FileFormat.com, I see there are disappointingly few fonts that support Georgian: http://www.fileformat.info/info/unicode/char/10b5/fontsupport.htm​​. You will not want to use any of the fonts that claim to support "all" of Unicode (Code2000) nor a fallback font (Unicode BMP Fallback; it will only display a character code), which only leaves DejaVu (sans), Everson Mono (typewriter), and Free Sans/Free Serif. For more choices, you'll have to look around the web.