Can't edit/select all text

Your text is broken to separate lines. Ypu can do one of this:
1. Use the script like Monika suggests.

2. Cut the text pieces from the lines and past them into the first one.

3. Convert all text lines into Area type (Type > Convert to Area Type), connect all lines (click on the Out marker — big square on the right side of the text area — and then click on the next line's In marker — big square on the right side of the text area)/ It's important here to be careful to the lines order. Then delete all other lines but the first one and change its size to see the whole text.

4/ If you have the original PDF file, open it in Acrobat (Reader or Professional), select the text by Type tool, copy it and paste in the first line in the AI file. Delete all other lines. Convert the Point Type to the Area Type, Change the area size as you need.

Do a web search for a merge text block javascript, there's a few different ones out there.

Is this a PDF?

Then you have the text cut in pieces. That's just what happens with PDFs. Illustrator is not a general purpose PDF editor.

https://prepression.blogspot.com/2014/09/the-ten-commandments-of-pdf.html