What is the XLSX format?

1What is an XLSX file?

XLSX is the Microsoft Excel workbook format since 2007. A workbook can have several sheets, and each sheet is a grid of cells containing numbers, text, dates or formulas. Besides the content, the file stores each cell's formatting, column widths, charts, pivot tables, filters and defined names.

It is the working tool for budgets, inventories, payroll, calendars, customer lists or data analysis. LibreOffice Calc and Google Sheets can open it too, although some advanced features may behave differently.

2How does Excel store data inside an XLSX?

Like DOCX, an XLSX is a ZIP package of XML files. Each sheet is a separate XML file that lists the cells with their values and formulas. Repeated text is stored only once in a shared string table to save space, and cell styles are defined in another file and reused. Charts and images are stored as separate parts inside the package.

Important: the file stores both the formula and the last calculated result. That is why a program that reads the file without calculating may show the saved value, while Excel recalculates on opening if needed.

• Sheets: one XML file each inside the package.
• Formulas: stored as text along with their value.
• Styles: defined once and reused by many cells.

3XLSX vs. XLS, XLSM and CSV

XLS is the older binary format, limited to 65,536 rows per sheet. XLSX replaced it with a maximum of 1,048,576 rows and 16,384 columns, and it is lighter and more open. XLSM is an XLSX that can include VBA macros; the regular XLSX doesn't save them. XLSB is a binary format that opens very large workbooks faster.

CSV is something else: plain text with values separated by commas or semicolons. It doesn't store formulas, formatting, colors or multiple sheets, but it is ideal for exchanging data between systems. If you need to keep formulas and formatting, use XLSX; if you only need the data to import into another program, use CSV.

4XLSX vs. PDF: when to use each one

Keep the XLSX as long as you need to calculate, filter or update data. When you are going to send a report, quote or invoice that shouldn't be altered, convert it to PDF: that way nobody accidentally changes a formula or sees data from other sheets. With “Office to PDF” you can generate a PDF of your workbook right on your device.

Before converting, check the print area, the sheet orientation and the scale. A wide sheet that doesn't fit on the page will be split across several; fit it to one page wide so the PDF looks tidy. And if the PDF turns out heavy because of images, “Compress PDF” helps.

5Common problems with XLSX files

The most frequent are numbers displayed as text, dates that change depending on regional settings, broken references when sheets are moved or deleted, external links that ask to be updated, and files that are heavy because they carry formatting across thousands of empty rows. There are also damaged-file warnings after an unexpected shutdown.

To slim down a workbook, delete unused rows and columns, avoid huge images and don't apply formatting to entire sheets. Before sharing it, make sure no links to paths on your computer remain and that the formulas don't depend on files the recipient doesn't have.

6Privacy tips when sharing an XLSX

An Excel workbook can hide more than it shows: hidden sheets, hidden columns, comments, author details, pivot tables with source data, and links to other files. Hiding is not protecting. If you are going to send it outside, review every sheet and consider exporting only what's needed to PDF.

With Rayo PDF GO you can convert to PDF on your device, so data such as payroll, customer lists or balance sheets doesn't pass through external servers. Afterward you can password-protect the PDF or number its pages.

7How to get the most out of XLSX in Rayo PDF GO

The usual approach is to calculate in XLSX and deliver in PDF. Set up the sheet with a clear print area, titles that repeat on every page, and a scale that fits the columns; then use “Office to PDF” to generate the document. A multi-sheet report can come out as several PDFs that you then join with “Merge PDF.”

If the PDF will be used for an official submission or an email, run it through “Compress PDF.” And if it contains personal data, “Protect PDF” adds a password before you send it. For a large list that someone else needs to keep processing, though, it is better to share the XLSX or a CSV, because the PDF doesn't keep the formulas.