I entered some text (T) in pdf in one column. Then I get the hand for moving and can no long enter text. I click on the T and nothing changes.
Writer simply is not a program to edit PDF documents.
And .pdf documents are not supposed to be edited. That’s why people trust them.
If you opened a PDF in LO, it is handled by Draw as a graphics page. It can then be edited, element by element, but certainly not as a text document.
If you’re getting a hand symbol then you are probably in Adobe Reader, not LO.
If you have created a Hybrid PDF and want to edit it in Writer again then open the pdf from within Writer, File » Open. In Windows you can also right click on the file in file explorer and select Open with…