function onOpen(e) {
    DocumentApp.getUi()
        .createMenu('Copy active Range.')
        .addItem('Copy Button', 'Copy')
        .addToUi();
}

function Copy() {
    var ss = DocumentApp.getActiveDocument();
    var selection = ss.getSelection();

    var tss = SpreadsheetApp.openById("xxx");
    var ts = tss.getSheetByName("name");

    trange = ts.getRange("B6:B6")
    selection.copyto(trange);
}

var SPREADSHEET_ID; // = assign your spreadsheet id to this variable
var SHEET_NAME; // = assign your sheet name to this variable

function onOpen(e) {
    DocumentApp.getUi()
        .createMenu('Copy active Range.')
        .addItem('Copy Button', 'Copy')
        .addToUi();
}

function Copy() {
    var ss = DocumentApp.getActiveDocument();
    var selection = ss.getSelection();

    var tss = SpreadsheetApp.openById(SPREADSHEET_ID);
    var ts = tss.getSheetByName(SHEET_NAME);

    trange = ts.getRange(2, 6); //I think, you can use B6 also
    trange.setValue(String(selection));
}