pdf to odt converter

You do not have the ODT anymore? You should have kept it...

To get a text file, you can use 'pdftotext' in a terminal, which is installed by default (at least on the GNOME edition of Trisquel):
$ pdftotext file.pdf
or, if there is some kind of layout (columns, hyphenations) to preserve:
$ pdftotext -layout file.pdf

Now the PDF coming from LibreOffice, it is possible it embeds the ODT: https://wiki.documentfoundation.org/Faq/Writer/PDF_Hybrid

If so, you can get the ODT back: install the "libreoffice-pdfimport" package (in Trisquel's repository) if it is not (but, then, there is no hope unless another copy of LibreOffice created the PDF) and drag-drop the PDF in LibreOffice.

Thank you Magic Banana!
I know i should have ketp my odt file of libreoffice but i dont know where i have placed it. It was my curriculum. Maybe i have deleted it accidentally i dont know. It is a bit old that document. Anyway i already learned to not make that mistake again LOL....
Thank you again , it was useful to learn the pdftotext thing, it saved me time to put the text onto another document. That was great :D

Try opening the PDF from Libreoffice. As magic banana said it's possible the odt is embedded in the pdf in which case the odt should be the one read by Libreoffice

Thank you davidnotcoulthard. My problem is already solved. Please consider this topic closed. Thank you very much.