Can it automatically establish footnote relationships between static footnote text and the main text

Hi @dublove try this script. - Mark

/**
 * @file Link Fake Footnotes with Fake Sources.js
 *
 * Create real footnotes (source reference and actual footnote)
 * from fake footnote sources and fake footnotes.
 *
 * Usage:
 *  1. place cursor into story
 *  2. run script.
 *
 * Requirements:
 *   - must have fake sources styled with a character style (see settings).
 *   - must have fake footnotes styled with a paragraph style (see settings).
 *
 * @author m1b
 * @version 2025-07-25
 * @discussion https://community.adobe.com/t5/indesign-discussions/can-it-automatically-establish-footnote-relationships-between-static-footnote-text-and-the-main-text/m-p/15429016
 */
function main() {

    var settings = {
        fakeSourceCharacterStyleName: 'Source',
        fakeSourceParagraphStyleName: 'myfooter',
        matchFakeSourceNumberGrep: '\\[\\d+\\]',
        matchFakeFootnoteNumberRegexp: /^\[\d+\]\s*/,
    };

    var doc = app.activeDocument;

    if (
        0 === doc.selection.length
        || 'InsertionPoint' !== doc.selection[0].constructor.name
    )
        return alert('Please place your insertion point into a story and try again.');

    // get the styles
    var sourceStyle = getThing(doc.allCharacterStyles, 'name', settings.fakeSourceCharacterStyleName);

    if (!sourceStyle)
        return alert('Did not find any character style "' + settings.fakeSourceCharacterStyleName + '".');

    var footerStyle = getThing(doc.allParagraphStyles, 'name', settings.fakeSourceParagraphStyleName);

    if (!footerStyle)
        return alert('Did not find any paragraph style "' + settings.fakeSourceParagraphStyleName + '".');

    // document footnote options (see https://www.indesignjs.de/extendscriptAPI/indesign-latest/index.html#FootnoteOption.html)
    doc.footnoteOptions.properties = {
        footnoteTextStyle: footerStyle,
        markerPositioning: FootnoteMarkerPositioning.NORMAL_MARKER,
        prefix: '[',
        separatorText: '\t',
        showPrefixSuffix: FootnotePrefixSuffix.PREFIX_SUFFIX_BOTH, // or FootnotePrefixSuffix.PREFIX_SUFFIX_REFERENCE,
        suffix: ']',
    };

    // collect the fake footnote sources
    var fakeSources = getTexts({
        items: doc.selection[0],
        findGrepPreferences: { findWhat: settings.matchFakeSourceNumberGrep, appliedCharacterStyle: sourceStyle },
    });

    if (0 === fakeSources.length)
        return alert('Did not find any fake footnote sources styled with "' + settings.fakeSourceCharacterStyleName + '".');

    // collect the fake footnotes
    var fakeFootnotes = getTexts({
        items: doc.selection[0],
        findGrepPreferences: { findWhat: '^.*(?:\\r?|$)', appliedParagraphStyle: footerStyle },
    });

    if (0 === fakeFootnotes.length)
        return alert('Did not find any fake footnotes styled with "' + settings.fakeSourceParagraphStyleName + '".');

    var len = Math.min(fakeSources.length, fakeFootnotes.length);
    var story = fakeSources[0].parentStory;

    // create a temporary text frame for the fake footnotes
    var tempFrame = story.textContainers[0].parentPage.textFrames.add({ contents: '\r' });
    var tempStory = tempFrame.texts[0].parentStory;

    // move the fake footnotes to the temporary frame
    for (var i = len - 1; i >= 0; i--)
        fakeFootnotes[i].move(LocationOptions.AT_BEGINNING, tempStory);

    for (var i = len - 1, footnote, fakeSource, fakeFootnote, index, start, end; i >= 0; i--) {

        fakeSource = fakeSources[i];
        fakeFootnote = tempStory.paragraphs[i];

        index = fakeSource.index;
        fakeSource.contents = '';

        // make a new footnote
        footnote = story.footnotes.add(
            LocationOptions.AFTER,
            fakeSource.parentStory.insertionPoints[index]
        );

        // identify the start and end of the footnote's actual text, after the number and before carriage return
        start = (fakeFootnote.contents.match(settings.matchFakeFootnoteNumberRegexp) || [[]])[0].length;
        end = ('\r' === fakeFootnote.characters.lastItem().contents) ? fakeFootnote.contents.length - 2 : fakeFootnote.contents.length - 1;

        // add the text from the fake footnote to the real footnote
        fakeFootnote.characters.itemByRange(start, end).move(LocationOptions.AT_END, footnote.texts[0]);

    }

    // clean up
    tempFrame.remove();

};
app.doScript(main, ScriptLanguage.JAVASCRIPT, undefined, UndoModes.ENTIRE_SCRIPT, 'Link Fake Footnotes');

/**
 * Returns texts found in `items`.
 *
 * Note: this is intended to use with
 * findGrep - it won't work without
 * a `findGrepPreferences` object.
 * ----------------------------------------------
 * Example - styled paragraphs of document:
 *
 *   var texts = getTexts({
 *     items: doc,
 *     findGrepPreferences: {
 *         appliedParagraphStyle: 'My Style',
 *     },
 *   });
 * ----------------------------------------------
 * @author m1b
 * @version 2024-04-24
 * @param {Object} options
 * @param {*} options.items - the DOM objects to extract text from, eg. Document or Document.selection.
 * @param {Object} options.findGrepPreferences - properties to configure findGrep.
 * @param {Function} [options.filter] - function that, given the object, returns true to collect its text (default: no filter).
 * @returns {Array<Text>}
 */
function getTexts(options) {

    options = options || {};

    if (undefined == options.items)
        throw Error('getTexts: expected `options.items` parameter.');

    if ('undefined' == options.findGrepPreferences)
        throw Error('getTexts: expected `options.findGrepPreferences` parameter.');

    var items = options.items,
        texts = [];

    if ('Document' === items.constructor.name)
        items = items.stories;

    if (!items.hasOwnProperty(0))
        items = [items];

    // set up find grep
    app.findGrepPreferences = NothingEnum.NOTHING;
    app.changeGrepPreferences = NothingEnum.NOTHING;

    for (var key in options.findGrepPreferences)
        if (options.findGrepPreferences.hasOwnProperty(key))
            app.findGrepPreferences[key] = options.findGrepPreferences[key];

    for (var i = 0; i < items.length; i++) {

        if (
            undefined != options.filter
            && true !== options.filter(items[i])
        )
            continue;

        if ('InsertionPoint' === items[i].constructor.name)
            items[i] = items[i].parentStory.texts[0];

        if (
            undefined != items[i].contents
            && 0 === items[i].contents.length
        )
            continue;

        if ('function' !== typeof items[i].findGrep)
            continue;

        texts = texts.concat(items[i].findGrep());

    }

    return texts;

};

/**
 * Returns a thing with matching property.
 * If `key` is undefined, evaluate the object itself.
 * @author m1b
 * @version 2024-04-21
 * @param {Array|Collection} things - the things to look through.
 * @param {String} [key] - the property name (default: undefined).
 * @param {*} value - the value to match.
 * @returns {*?} - the thing, if found.
 */
function getThing(things, key, value) {

    for (var i = 0; i < things.length; i++)
        if ((undefined == key ? things[i] : things[i][key]) == value)
            return things[i];

};