Edit single sentence, not an entire paragraph.

I have 3 sentences, one under the other. Each sentence was created using the Add Text tool. Each sentence was created in a independently of the other two.

When I preveiw the document I see the three sentences. When I revert back to edit, I see three sentences are each bound in separate box. I close the edit function, save the document, then close the document.

When I reopen the document and edit, the three sentences are now bound together in the same edit box.

How do I keep adobe acrobat pro dc from merging all the sentences into the same editing box?