Recently a bug appeared in PDF-commenting.
Suppose you have "1-2" and want to change it to "1 and 2". The way that used to work was this: select the dash and insert a comment with replace text " and " (with blanks before and after). And it worked - importing and applying it in Indesign resulted "1 and 2", as expected. But now those blanks disappear as soon as posting the comment in Acrobat (and it does the same in Acrobat Reader too), so the end result is "1and2", which is definitely wrong!
And if you have to correct "twowords", put the insertion point between o and w, comment with inserting text, type a blank and post the comment... at least that's how worked in good old days. Now the "Post" button is greyed out if in the comment there's just a blank.