How to convert pdf files to ODP

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The short answer is that you can't "use Abobe reader in Libre Office".

However, depending on what that PDF contains, you have a few possibilities:

• from your (very brief) description I expect the PDF has images? You can extract the images (which tool you use depends on your operating system, which information you haven't included in your question) and go from there.
• LibreOffice Draw can load PDF files, and you could use Draw to attempt to open your PDF.
• if the PDF has text, Adobe Reader will let you save the file as .txt, and you can get at the text content that way.

We need more information to give more help, but hopefully this is a start.