CSV is just text: one row per line, cells separated by commas. Every system exports it and every system imports it. XLSX is Microsoft’s format: multiple sheets, formatting, formulas, dates that know they are dates. Converting between them is a daily task, and three things regularly go wrong.

1. Leading zeros disappear

A postcode like 02139 or a product code like 000451 becomes 2139 and 451 when Excel decides the column is numeric. If the codes matter, keep them as text before converting, or fix the column type after.

2. Dates change shape

CSV has no idea what a date is; it is just characters. 03/04/2026 is 3 April in most of the world and 4 March in the US. Convert Files keeps the text exactly as it was, so what you see is what was written — but check the convention before you trust a column.

3. Only the first sheet is exported

CSV can hold one table. Converting a workbook with five sheets to CSV gives you the first one. If you need all of them, convert to .pdf or .docx instead, which puts every sheet in as its own table.

Beyond Excel

The same data also converts to JSON for developers, to SQL insert statements for a database, to Markdown for documentation, and to ODS for LibreOffice.