Office.cs

using System.Collections.Generic;
using System.IO;
using System.Linq;
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Spreadsheet;
using DocumentFormat.OpenXml.Wordprocessing;

public static class Office
{
    public static IEnumerable<string> GetExcelText(Stream stream)
    {
        using var doc = SpreadsheetDocument.Open(stream, false);
        var sst = doc.WorkbookPart.GetPartsOfType<SharedStringTablePart>().First()
            .SharedStringTable.ChildElements.Select(x => x.InnerText)
            .ToArray();
        foreach (var sheet in doc.WorkbookPart.Workbook.Descendants<Sheet>())
        {
            var part = (WorksheetPart)doc.WorkbookPart.GetPartById(sheet.Id);
            foreach (var cell in part.Worksheet.Descendants<Cell>())
            {
                switch (cell.DataType?.Value)
                {
                    case CellValues.Boolean:
                        yield return cell.InnerText == "0" ? "false" : "true";
                        break;
                    case CellValues.SharedString:
                        yield return sst[int.Parse(cell.InnerText)];
                        break;
                    case CellValues.Date:
                        yield return cell.InnerText;
                        break;
                }
            }
        }
    }

    public static IEnumerable<string> GetWordText(Stream stream)
    {
        using var doc = WordprocessingDocument.Open(stream, false);
        foreach (var element in doc.MainDocumentPart.Document.Body)
        {
            if (element is Paragraph p)
            {
                yield return p.InnerText;
            }
        }

        var comments = doc.MainDocumentPart?.WordprocessingCommentsPart?.Comments;
        if(comments == null)
            yield break;
        foreach (var element in comments)
        {
            yield return element.InnerText;
        }
    }
}