In a sheet cell you can show a reference to a cell in another sheet.
In the same way, a reference can also be made to a cell from another document provided that this document has already been saved as a file.
Open a new, empty spreadsheet. By default, it has only a single sheet named Sheet1. Add a second sheet clicking on + button to the left of the sheet tab in the bottom (it will be named Sheet2 by default).
By way of example, enter the following formula in cell A1 of Sheet1:
Click the Sheet 2 tab at the bottom of the spreadsheet. Set the cursor in cell A1 there and enter text or a number.
If you switch back to Sheet1, you will see the same content in cell A1 there. If the contents of Sheet2.A1 change, then the contents of Sheet1.A1 also change.
When referencing a sheet with name containing spaces, use single quotes around the name: ='Sheet with spaces in name'.A1
The example uses Calc formula syntax. It is also possible to use Excel A1 or R1C1 formula syntax; this is configured on Formula options page.
Choose File - Open, to load an existing spreadsheet document.
Choose File - New, to open a new spreadsheet document. Set the cursor in the cell where you want to insert the external data and enter an equals sign to indicate that you want to begin a formula.
Now switch to the document you have just loaded. Click the cell with the data that you want to insert in the new document.
Switch back to the new spreadsheet. In the input line you will now see how LibreOffice Calc has added the reference to the formula for you.
The reference to a cell of another document contains the name of the other document in single inverted commas, then a hash #, then the name of the sheet of the other document, followed by a point and the name of the cell.
Confirm the formula by clicking the green tick.
If you drag the box in the lower right corner of the active cell to select a range of cells, LibreOffice automatically inserts the corresponding references in the adjacent cells. As a result, the sheet name is preceded with a "$" sign to designate it as an absolute reference.
If you examine the name of the other document in this formula, you will notice that it is written as a URL. This means that you can also enter a URL from the Internet.