Coming from EPPlus 4.x

EPPlus 4.x edits workbooks through ExcelPackage, ExcelWorkbook, ExcelWorksheet and ExcelRange. OneDocument's workbook is Workbook / Worksheet / Cell. (Later EPPlus versions have a different licence and are not covered.) Read README.md first for what is true on every page.

Open, read, write, save

// EPPlus 4.x
using var package = new ExcelPackage(new FileInfo(path));
ExcelWorksheet ws = package.Workbook.Worksheets["Sales"];
object v = ws.Cells["B2"].Value;
ws.Cells["B2"].Value = 1200;
ws.Cells["A2"].Value = "North";
package.Save();

// OneDocument
using Workbook wb = Workbook.Open(path);
Worksheet ws = wb.Sheets["Sales"];
CellValue v = ws["B2"].Value;          // .Text, .Number, .FormattedText read it other ways
ws["B2"].Value = 1200;
ws["A2"].SetString("North");
wb.Save();                              // atomic replace; only the edited sheet part changes

A new workbook: ExcelPackage() + Worksheets.Add("Sales") becomes Workbook.Create() + wb.Sheets.Add("Sales"). Save to a stream with wb.SaveAs(stream, OfficeFormat.Xlsx); SaveAs(path) picks the format from the extension.

Formulas and calculation

// EPPlus 4.x
ws.Cells["B5"].Formula = "SUM(B2:B4)";
package.Workbook.Calculate();

// OneDocument
ws["B5"].Formula = "SUM(B2:B4)";       // no leading '='
wb.Recalculate();                       // incremental; wb.RecalculateAll() for everything

The calculation engine is OneDocument's own (spill, LET, LAMBDA, structured references). Settings such as iteration are on the workbook (SetIterativeCalculation). docs/spreadsheets-calc.md lists what is calculated and the documented deviations.

Styles and number formats

// EPPlus 4.x
ws.Cells["A1"].Style.Font.Bold = true;
ws.Cells["B2"].Style.Numberformat.Format = "#,##0.00";

// OneDocument
ws.Range("A1").UpdateStyle(s => s with { Font = (s.Font ?? new CellFont()) with { Bold = true } });
ws.Range("B2").NumberFormat = "#,##0.00";

Styles are immutable records (CellStyleSpec); UpdateStyle returns a new one, for a cell (ws["A1"].UpdateStyle) or a block (ws.Range("A1:C3").UpdateStyle). ws["A1"].FormattedText gives the text as Excel displays it.

Tables, names, merges, dates

// EPPlus 4.x
ws.Tables.Add(ws.Cells["A1:D10"], "Orders");
ws.Cells["A1:C1"].Merge = true;
ws.Cells["C2"].Value = new DateTime(2026, 3, 1);

// OneDocument
ws.Tables.Add("Orders", CellRange.Parse("A1:D10"));
ws.Range("A1:C1").Merge();
ws["C2"].SetDate(new DateTime(2026, 3, 1));
wb.Names.Add("Rate", "Sales!$B$1");

Conditional formatting and data validation are ws.ConditionalFormats and ws.Validations (docs/spreadsheets-styles.md).

Loading collections

// EPPlus 4.x
ws.Cells["A1"].LoadFromCollection(orders, true);

// OneDocument: mark the type [SpreadsheetRow] (a partial class or record), then
Spreadsheet.Write(path, orders);                     // or .csv, .tsv
foreach (Order o in Spreadsheet.Read<Order>(path)) { }

The binding is generated at compile time (no reflection) and streams: see docs/spreadsheets-poco.md. To write the same data into a sheet of an open workbook, loop and set cells.

Streaming

EPPlus 4.x has no streaming reader or writer. OneDocument has XlsxStreamReader / XlsxStreamWriter (constant memory, no allocation per cell on read): docs/spreadsheets-streaming.md.

PDF

EPPlus 4.x does not render. wb.SaveAs("report.pdf") or Office.Convert("in.xlsx", "out.pdf") does, with the Rendering package.

Not supported or different

• ws.Range("A1:C3") is a handle with Values (a two-dimensional array), UpdateStyle, NumberFormat, Clear and Merge; there is no Copy, AutoFitColumns or LoadFromCollection on it (use Spreadsheet.Write for rows of objects).
• ws.AddPicture(bytes, "E1", ...) adds a picture. Charts are not created through a high-level call; existing ones are kept and rendered.
• No sparkline, form control or shape creation API.
• Password protection: sheet and workbook protection are supported (docs/protection.md); encrypted files are written only as XLS (RC4) for now.
• Cell values are CellValue (kind plus payload), not object; strings are handles into the workbook's string table, hence SetString.
• Rows and columns are 1-based on both sides; ws[row, column] mirrors Cells[row, column].
• Templates: EPPlus 4.x has none; see docs/templating-xlsx.md.