XLS files are binary Excel workbooks compatible with older versions of Microsoft Office.
Common Uses
Working with legacy Excel files
Compatibility with older systems
Spreadsheet data storage
XLS Transformation FAQ
What is an XLS document?
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XLS is a spreadsheet format. It stores tabular data with formulas, cell formatting, charts and pivot-table references. Converting XLS to CSV strips everything but the raw cell values, which is exactly what you want for data import; converting to PDF preserves the look-and-feel for sharing. XLS is still what a great deal of legacy financial and government reporting tooling emits and expects.
Do formulas survive when I convert an XLS?
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Only into another real spreadsheet format. Convert XLS to a spreadsheet and formulas, references and named ranges round-trip intact. Convert to a flat data or page format and every cell is frozen at its last computed value — the number stays, the calculation behind it does not. That is usually what you want for sharing and never what you want for continued work. An XLS is an OLE compound file holding sheets, formulas, formatting and any VBA macros as binary streams.
Why is XLS the format everyone at work sends?
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Because it is what the software on the machine saves by default, and defaults decide almost everything about which formats spread. The awkward cases are the predictable ones: a recipient on different software, an older version, or a system that only accepts one specific format for upload. All three are one conversion away from working. XLS is the binary Microsoft Excel workbook format from Excel 97 through Excel 2003.
Why does newer software warn me when I open an XLS?
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Because it is the pre-2007 binary format, and binary Office documents are a well-known malware delivery route — the warning is about the container, not about your file. The modern replacement is a zipped XML package that is safer to parse, smaller on disk and readable by tools that are not Microsoft's. Converting is the way out of the warning, and the content survives it intact. XLS caps out at 65,536 rows and 256 columns, and its macro payloads make it a recurring security problem.
What if my XLS is a scan rather than real text?
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Then nothing downstream can read it until OCR has run. A scanned page is a picture of words: it looks fine, and searching, copying or converting to an editable document all come back empty. Optical character recognition adds a real text layer over the image, after which the words are selectable and the conversion produces an actual document instead of a wrapper around a photograph.
Why is an XLS so awkward to read on a phone?
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Because a grid cannot reflow. Text rewraps to a narrow screen; a row of eighteen columns cannot, so the choice is scrolling sideways or shrinking everything until the numbers are unreadable. Converting to a fixed page keeps the grid and makes zooming predictable; converting to a document turns each sheet into a table that reads properly in one column, at the cost of being able to recalculate anything.
Should I still be saving new files as XLS?
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Only if something downstream demands it. The format still opens, and there is no urgency about converting an archive that is not causing trouble, but it is no longer where the tooling or the efficiency is going. For anything new, a current format costs nothing extra and avoids the next round of this question a few years from now.
Are cell references between sheets kept when converting XLS?
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Between real spreadsheet formats, yes — cross-sheet references, named ranges and defined formats travel with the file. Anything flatter than a spreadsheet has no concept of a reference, so it stores the value the reference resolved to at the moment of conversion. A workbook that pulls from other files should be checked after conversion rather than assumed correct.
What is the best format to convert XLS to?
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For sharing without edits, convert XLS to PDF — every device opens it the same way. For further editing, convert to DOCX. For data extraction from spreadsheets, convert to CSV.
Does converting XLS preserve formatting?
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When you convert XLS to a similar document format (Word, ODT, PDF), formatting, fonts, images and tables are preserved with high fidelity. When you convert to a plain-text format (TXT, MD), styling is stripped down to the underlying words.
