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 leave you guessing which matches actually changed. This changes the words in the file, in the font they were already set in, and it tells you what it will and will not touch before you commit.
Because it changes real text, some matches cannot be changed in place — and rather than skip them quietly, it counts them and says so. A match that runs across a line break, or across a change of font in the middle, is stored as separate pieces the tool will not rewrite together, because a half-finished replacement across those pieces would look worse than an honest “not this one”. A match it cannot trace to a definite spot in the file is held back the same way. You see the number before you press the button, so the count never overstates what will happen.
A replacement that fits the space of the words it replaces goes in cleanly, in their own font. A replacement long enough to run over the surrounding layout is flagged instead of forced, because there is nothing worse than a fix that quietly pushes the rest of the line off the page.
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.