It depends. I’ve proofread a letter recently, and while it was a casual letter, nothing legal, or anything the like, the contractions simply looked out of place against the overall style. A text usually should look “as if made from one piece” in the end. That could mean getting rid of all contractions, contracting anything that can be contracted, or mix’n’match.
Typically, writers, editors, proofreaders should be able to get it right, especially with longer texts. If someone provides just a short text, checking other existing material (and the nature of the text/entity/…) should provide clues. (Let us not get into the tangential discussion about how customers should either provide enough clues themselves or alternatively cover the additional time needed for the checking/how sellers should include it in their offers, though).
However, there are also proofreaders who desperately want to, need to, correct something, to p̶r̶o̶o̶f̶ prove their worth, even if there might be nothing to correct, and while there are awesomely awesome proofreaders who really improve things by whole levels, there are also proofreaders who ruthlessly destroy what writers, translators, editors did on purpose, and ruin style and atmosphere.
If you’re happy with a proofreader and think they have a good grasp of not just their job but also your style and everything, chances are that they do the right thing; if you’re not so sure, maybe ask them and see what they say, and if you can agree, or not.
You could also ask someone, or several someones (ideally the kind of people who might, or do consume your writing), to read that same text, once with, once without contractions, without any additional info (such as which one is your original text, which one the proofread one, and without any kind of evaluative wording), and ask how they feel about it. Proofreaders might feel one way about it, while the vox populi might feel different.
And lastly, your own feelings, of course, aren’t the least important; even if your proofreader or your test reader(s) would give you reasons you can understand, but it still looks weird to you, as the author, you could also decide that it’s your style or even trademark, and keep doing it, it’s your text, after all, and the “accept(all)/dismiss” feature is implemented in Word for a reason.
That said, of course, you shouldn’t fight your proofreaders, editors, or other helpful people over actual facts, or over things they can explain well enough to convince you… unless the facts are facts but you still know that all your readers will know that your character, or even you as the narrator, not weak in grammar is but a Yoda reference you made, and your helpful person can’t tell ST from SW. Or if you don’t know but don’t care either
In summary, my take depends.