If you are on Windows and have Acrobat Pro (not reader), you can try the old Component Object Model with Python or VBA.

import win32com, winerror, os
from win32com.client.dynamic import ERRORS_BAD_CONTEXT
ERRORS_BAD_CONTEXT.append(winerror.E_NOTIMPL)
win32com.client.gencache.EnsureModule('{E64169B3-3592-47d2-816E-602C5C13F328}', 0, 1, 1)
avDoc = win32com.client.DispatchEx('AcroExch.AVDoc')
avDoc.Open(src, src)
avDoc.BringToFront()
pdDoc = avDoc.GetPDDoc()
jsoObject = pdDoc.GetJSObject()
for pageNo in range(1):
pdfPage = pdDoc.AcquirePage(pageNo)
pageHL = win32com.client.DispatchEx('AcroExch.HiliteList')
_ = pageHL.Add(0, 9000)
pageSel = pdfPage.CreatePageHilite(pageHL)
pdfText = ""
for wordNo in range(pageSel.GetNumText()):
word = pageSel.GetText(wordNo)
pdfText += word
if keyword in pdfText:
wordToHl = win32com.client.DispatchEx('AcroExch.HiliteList')
wordToHl.Add(wordNo, 1)
wordHl = pdfPage.CreateWordHilite(wordToHl)
rect = wordHl.GetBoundingRect()
annot = jsoObject.AddAnnot()
props = annot.GetProps()
props.Type = "Square"
props.Page = pageNo
props.Hidden = False
props.Lock = True
props.Name = word
props.NoView = False
props.Opacity = 0.3
props.ReadOnly = True
props.Style = "S"
props.ToggleNoView = False
props.PopupOpen = False
popupRect = [rect.Left - 5, rect.Top + 5, rect.Left + 40, rect.Top - 20]
props.Rect = popupRect
props.PopupRect = popupRect
props.StrokeColor = jsoObject.Color.Red
props.FillColor = jsoObject.Color.Yellow
annot.SetProps(props)
print(f'Found {keyword}')