Need training on a document whose original *I created*! How to edit "text boxes" as *entire boxes* n

I opened a document in Acrobat Premium on my iPad. I selected it for "Edit PDF". All was fine and dandy. Then I tapped another paragraph. A text box formed around *three words* in that paragraph (not the entire paragraph, as I had hoped). When editing I inserted characters and the remainder of the (existing) character string in the text box overflowed the box and overlaid text outside the box. This makes Acrobat essentially useless for me, in editing text. N.b., this is a PDF *I* created elsewhere, intact, and so should have no hidden discrete text boxes. It seems I am far short in my knowledge of the nature of PDFs or proper use of Acrobat Premium. Advice requested.