Files above ~2 GB aren’t supported in the current version due to .NET runtime constraints on in-memory buffers. This applies to any source format, not just XLSX.
A few approaches that typically resolve it:
Split the workbook into smaller XLSX files (for example, by sheet or by row range), convert each part to PDF, then merge the resulting PDFs.
Reduce the file size at the source. Very large XLSX files are often inflated by embedded images, heavy formatting, or unused cached ranges. Opening the file in Excel and re-saving after cleanup frequently brings it well under the
limit.
Run in a 64-bit process with sufficient RAM. Peak memory during conversion is several times the source file size, so headroom matters even for files under 2 GB.
If you can share a bit more about the file — sheet count, approximate row count, whether it contains many images or embedded objects — we’d be glad to suggest a more targeted split strategy.