The job is almost always the same: a name has changed, a date was wrong, a price was quoted twice and only one of them got fixed. What makes it tedious is not the typing but the counting — you fix four, miss the fifth, and find it a week later in the copy that went out.
Find and replace exists so the fifth one cannot be missed. Type what you are looking for, see every match with a count, type the replacement, and change them together. What differs here is what happens at the moment of commitment.
Most tools that offer replacement in a PDF do one of two things: they put a white box over the old words and type on top, which shows the moment anyone opens the file somewhere else, or they substitute a font that is nearly right, which shows in print. This changes the words in the file, in the font they were already set in.
Where that is not possible, you get told. A document may use a font that was embedded without every letter — common, and invisible until you type a character it does not contain. When that happens the matches are grouped by font, and you make one decision per font rather than one per match: eight replacements across three fonts is three questions. The substitute is previewed on your own words before anything is committed, and your choice is remembered for that font.
Two smaller honesty details. Matches found on scanned pages are shown and skipped, so the count never lies about what will change. And undo puts back the whole replacement in one step, because replacing was one action — reversing it forty times would be a strange way to treat a mistake.
Free, no signup, and no cap on how many matches you replace or how long the document is.