exceltopdf-service/Services/ExcelToPdfService.cs

using Syncfusion.XlsIO;
using Syncfusion.XlsIORenderer;

namespace ExcelToPdfService.Services;

public interface IExcelToPdfService
{
    Task<byte[]> ConvertAsync(Stream excelStream, string? printArea = null, bool landscape = false);
    Task<byte[]> ConvertFileAsync(string filePath, string? printArea = null, bool landscape = false);
}

public class ExcelToPdfService : IExcelToPdfService
{
    public Task<byte[]> ConvertAsync(Stream excelStream, string? printArea = null, bool landscape = false)
    {
        using var excelEngine = new ExcelEngine();
        var app = excelEngine.Excel;
        app.DefaultVersion = ExcelVersion.Xlsx;

        var workbook = app.Workbooks.Open(excelStream);
        return Task.FromResult(Convert(workbook, printArea, landscape));
    }

    public Task<byte[]> ConvertFileAsync(string filePath, string? printArea = null, bool landscape = false)
    {
        if (!File.Exists(filePath))
            throw new FileNotFoundException("Excel file not found", filePath);

        using var excelEngine = new ExcelEngine();
        var app = excelEngine.Excel;
        app.DefaultVersion = ExcelVersion.Xlsx;

        using var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read);
        var workbook = app.Workbooks.Open(fs);
        return Task.FromResult(Convert(workbook, printArea, landscape));
    }

    private static byte[] Convert(IWorkbook workbook, string? printArea, bool landscape)
    {
        var sheet = workbook.Worksheets[0];

        // Page setup
        sheet.PageSetup.FitToPagesWide = 1;
        sheet.PageSetup.FitToPagesTall = 0;
        sheet.PageSetup.Orientation = landscape
            ? ExcelPageOrientation.Landscape
            : ExcelPageOrientation.Portrait;

        if (!string.IsNullOrWhiteSpace(printArea))
            sheet.PageSetup.PrintArea = printArea;

        // Convert
        var renderer = new XlsIORenderer();
        var settings = new XlsIORendererSettings
        {
            LayoutOptions = LayoutOptions.Automatic
        };

        var pdf = renderer.ConvertToPDF(workbook, settings);

        using var ms = new MemoryStream();
        pdf.Save(ms);
        return ms.ToArray();
    }
}