In LibreOffice Writer, normal body text can't "remember" a page position — it just flows into the text at the cursor. To make text land at the exact same spot on a page in another document, it must be held in a page-anchored frame (or text box). Do this:

1. Put the text in a frame first (source document): select the text, then Insert ▸ Frame (in newer versions: Insert ▸ Frame ▸ Frame…). In the frame's properties, on the Type tab, set Anchor to To page and give it fixed Horizontal/Vertical position (e.g., "From left / From top" with your distances).
2. Copy the frame: click on the frame's border (so the frame itself, not the inner text, is selected) and press Ctrl+C.
3. Paste in the target document (Ctrl+V): because the frame is anchored To page with absolute coordinates, it reappears at the same position on the page it's pasted into — independent of the cursor location. This works across documents as long as both use the same page size/margins ( LibreOffice Help).

A few notes:

• The same works with text boxes (Insert ▸ Text Box): set their anchoring to "To page" and they also keep their position when copied.
• Caveat: a "To page" anchor pins the frame to one specific page (the page it was pasted on). If the target document grows, the frame stays glued to that page number.
• If both documents share the same page style (margins, size), the position will match exactly; otherwise it's relative to that document's own page edges.
• If you instead just want the text formatting preserved, use Ctrl+Shift+V (Paste Special) and choose "Formatted text [RTF]" — but that only preserves formatting, not page position.

If you meant something different — e.g., keeping your scroll position when switching between the two document windows — let me know and I'll address that instead.