Compress Documents Online
Reduce document file sizes with quality control settings - PDF, Word, Excel, PowerPoint
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How much each format actually shrinks
We ran the same engines this page uses in your browser over one test document and measured every result. The source was a report with headings, styled text, tables, lists and two photographs, so the numbers below show what compression can and cannot do for each format.
Source: one report document, converted to each format, then compressed with the engines this page runs in your browser.
| Format | How we compress it | Before | After | Saved | What that means |
|---|---|---|---|---|---|
| Ghostscript rebuild | 1082.3 KB | 178.4 KB | 83.5% | Images downsampled to the preset you pick | |
| HTML | Minify + gzip | 1331.6 KB | 997.5 KB | 25.1% | Strips comments and whitespace between tags |
| XLSX | ZIP repack, level 9 | 142.1 KB | 135.8 KB | 4.4% | Repetitive sheet data compresses a little further |
| DOCX | ZIP repack, level 9 | 997.5 KB | 997.9 KB | 0% | Already well compressed by Word; little left to take |
| ODT | ZIP repack, level 9 | 993.5 KB | 993.5 KB | 0% | Same story as DOCX |
| EPUB | ZIP repack, level 9 | 995 KB | 995.4 KB | 0% | Size is dominated by the cover and inline images |
| RTF | Whitespace minify | 2097.6 KB | 2097.6 KB | 0% | Convert to DOCX if size matters |
| CSV | Whitespace minify | 167.1 KB | 167.1 KB | 0% | Already minimal; zip it instead |
| TXT | Whitespace minify | 9.3 KB | 9.3 KB | 0% | Already minimal; zip it instead |
- PDF is where compression pays off. Rebuilding the file cut it from 1082.3 KB to 178.4 KB, a 83.5 reduction, because the images inside get downsampled.
- Office formats such as DOCX, ODT and EPUB are ZIP archives that the program already compressed when it saved them. Repacking them at maximum settings usually recovers only a few percent, and sometimes nothing at all.
- The exception is a file whose contents were stored without compression, which some exporters and older versions of Word produce. In that case the same repack cut a 413.4 KB document down to 11.3 KB.
- Plain-text formats such as TXT, CSV and RTF hold almost no slack. If you need them smaller, put them in a ZIP archive rather than compressing them in place.
What the PDF presets do
The four quality presets map to different image resolutions inside the PDF. On our test file Fast produced 343.2 KB, Normal 178.4 KB, Maximum 1007.8 KB and Ultra 1004.7 KB, from a 1082.3 KB source. Maximum and Ultra keep the original image resolution, so they save the least but preserve print quality.
Measured on one representative document. Your own files will differ, especially depending on how many images they contain and which program saved them.
Supported Document Formats
Compress all major document file types with adjustable quality settings
Word Processing
Microsoft Word's legacy binary format (Word 97-2003).
Converted to DOCX first, then repacked.
Old binary files usually shrink most on this path.
Microsoft Word's XML-based format, 2007 onward.
Every part is unpacked and repacked at maximum ZIP compression.
Files already saved well by Word barely move; poorly saved ones shrink a lot.
The OpenDocument text format from OASIS.
Unpacked and repacked at maximum ZIP compression.
Gains depend on how the original was written to disk.
Rich Text Format, Microsoft's portable text format.
Redundant whitespace is stripped from the markup.
RTF is plain text, so savings are modest unless it is heavily padded.
A Word document that carries VBA macros.
Repacked at maximum ZIP compression, macros untouched.
The macro project is preserved exactly.
The legacy Word template format (97-2003).
Repacked like any other Word container.
Template behaviour is unchanged.
The modern Word template format, 2007 onward.
Unpacked and repacked at maximum ZIP compression.
Styles and layout survive intact.
A Word template that also carries macros.
Repacked at maximum ZIP compression with macros kept.
Both the layout and the VBA project are preserved.
The native format of the AbiWord word processor.
Whitespace-minified, then re-gzipped at maximum level.
Compresses well because it is XML underneath.
Applix Word's format from the Applixware suite.
Minified and re-gzipped at maximum level.
A rare format, handled as compressed XML.
KWord's format from the old KOffice suite.
Unpacked and repacked at maximum ZIP compression.
Legacy KOffice documents open the same afterwards.
StarOffice Writer's format, the ancestor of ODT.
Repacked at maximum ZIP compression.
The document opens exactly as before.
Plain unformatted text, ASCII or Unicode.
Trailing spaces and repeated blank lines are removed.
Already about as small as text gets, so expect very little.
Spreadsheet
Excel's legacy binary workbook (97-2003).
Converted to XLSX first, then repacked.
Legacy binary sheets often shrink noticeably.
Excel's XML-based workbook, 2007 onward.
Sheet XML is unpacked and repacked at maximum compression.
Large sheets of repetitive data compress best.
The OpenDocument spreadsheet format.
Unpacked and repacked at maximum ZIP compression.
Formulas and cell formatting are preserved.
Plain-text rows with commas between values.
Trailing whitespace and blank lines are trimmed.
Already minimal, so savings are small.
Presentation
PowerPoint's legacy binary deck (97-2003).
Converted to PPTX first, then repacked.
Older decks with embedded media benefit most.
PowerPoint's XML-based deck, 2007 onward.
Slide parts are unpacked and repacked at maximum compression.
Decks dominated by photos are limited by the images themselves.
The OpenDocument presentation format.
Unpacked and repacked at maximum ZIP compression.
Slides and transitions are kept as-is.
Other Formats
Adobe's fixed-layout document format.
Rebuilt with Ghostscript, images downsampled to your preset.
This is where the largest savings happen, often well over half.
A format built for scanned pages and books.
Already uses aggressive scan-specific compression.
Little left to gain; it is near its floor by design.
Microsoft's fixed-layout answer to PDF.
Unpacked and repacked at maximum ZIP compression.
Convert to PDF if you want real size reductions.
The Ecma-standardised version of XPS.
Repacked at maximum ZIP compression.
Same handling as XPS.
Markdown, plain text with light formatting marks.
Trailing whitespace and extra blank lines are stripped.
Files are tiny already, so changes are marginal.
The markup language behind every web page.
Comments and whitespace between tags are removed.
Verbose exported HTML can shrink by a quarter or more.
The open e-book standard, built on HTML and CSS.
Unpacked and repacked at maximum ZIP compression.
Text-heavy books gain little; image-heavy ones are capped by their images.
References
- High Level Devices, including pdfwrite and PDFSETTINGS - Ghostscript documentation
- RFC 1951: DEFLATE Compressed Data Format Specification version 1.3 - RFC Editor
- RFC 1952: GZIP file format specification version 4.3 - RFC Editor
- APPNOTE.TXT: .ZIP File Format Specification - PKWARE
- ISO 32000-2:2020, Portable document format (PDF 2.0) - ISO
- ECMA-376: Office Open XML File Formats - Ecma International
- Compression Streams API - MDN Web Docs, Mozilla
- JSZip documentation