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GroupDocs.Comparison detects changes in text (paragraphs, words, characters), tables, images, and shapes across a wide range of formats — Word, PDF, Excel, PowerPoint, HTML, AutoCAD, Visio, Outlook, OpenDocument, images, and more. The full list is available on the Supported document formats page.

By default, GroupDocs.Comparison highlights detected changes with the following colours:

• Inserted – blue
• Deleted – red
• Style changed – green

These are the defaults — you can override colours, fonts, and other styling via the InsertedItemStyle, DeletedItemStyle, and ChangedItemStyle properties. See Customize changes styles for details.

To compare two documents, follow these steps:

1. Instantiate the Comparer object with source document path or stream.
2. Call the add() method and specify target document path or stream.
3. Call the compare() method. It returns the path of the result document.

import com.groupdocs.comparison.Comparer;
import java.nio.file.Path;
// ...

try (Comparer comparer = new Comparer("source.pdf")) {
    comparer.add("target.pdf");
    final Path resultPath = comparer.compare("result.pdf");
}

The output file is as follows:

import com.groupdocs.comparison.Comparer;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
// ...

try (InputStream sourceInputStream = new FileInputStream("source.docx");
     InputStream targetInputStream = new FileInputStream("target.docx");
     OutputStream resultOutputStream = new FileOutputStream("result.docx");
     Comparer comparer = new Comparer(sourceInputStream)) {
    comparer.add(targetInputStream);
    comparer.compare(resultOutputStream);
}

To control how the comparison is performed and how the result is rendered, pass a CompareOptions object to the compare() method. These options work with any supported document format:

import com.groupdocs.comparison.Comparer;
import com.groupdocs.comparison.options.CompareOptions;
// ...

try (Comparer comparer = new Comparer("source.docx")) {
    comparer.add("target.docx");

    CompareOptions options = new CompareOptions();
    options.setDetectStyleChanges(true);
    options.setGenerateSummaryPage(true);
    options.setShowDeletedContent(true);
    options.setShowInsertedContent(true);

    comparer.compare("result.docx", options);
}

For format-specific behaviour, GroupDocs.Comparison provides dedicated subclasses of CompareOptions:

• WordCompareOptions — Word-specific settings such as DisplayMode (REVISIONS / HIGHLIGHT), line-break marking, and bookmark comparison. See Word document comparison options.
• PdfCompareOptions — PDF-specific settings such as DisplayMode (INLINE / SIDE_BY_SIDE / INTERLEAVED), page-range filtering, image comparison, and PDF annotation author name. See Disable image comparison in PDF documents.

Using a format-specific subclass is recommended when comparing a known document type — it makes Word-only or PDF-only settings discoverable and prevents you from passing irrelevant options.

The example below compares only the first two pages of two PDF documents and lays the result out side by side:

import com.groupdocs.comparison.Comparer;
import com.groupdocs.comparison.options.PagesSetup;
import com.groupdocs.comparison.options.PdfCompareOptions;
// ...

try (Comparer comparer = new Comparer("source.pdf")) {
    comparer.add("target.pdf");

    PagesSetup pagesSetup = new PagesSetup();
    pagesSetup.setStartPage(1); // 1-based, inclusive; null means "from the first page"
    pagesSetup.setEndPage(2);   // 1-based, inclusive; null means "to the last page"

    PdfCompareOptions options = new PdfCompareOptions();
    options.setDisplayMode(PdfCompareOptions.ComparisonDisplayMode.SIDE_BY_SIDE);
    options.setPagesSetup(pagesSetup);

    comparer.compare("result.pdf", options);
}

While CompareOptions controls how documents are compared, LoadOptions controls how the source and target files are loaded into the Comparer. It is passed to the Comparer constructor and to add(), before any comparison runs.

import com.groupdocs.comparison.Comparer;
import com.groupdocs.comparison.options.load.LoadOptions;
import com.groupdocs.comparison.result.FileType;
// ...

LoadOptions loadOptions = new LoadOptions();
loadOptions.setFileType(FileType.DOCX);

try (Comparer comparer = new Comparer("source.docx", loadOptions)) {
    comparer.add("target.docx", loadOptions);
    comparer.compare("result.docx");
}

Common LoadOptions properties:

• Password — open a password-protected source or target document. See Load password-protected documents.
• FileType — specify the document format explicitly and skip auto-detection (faster for large files). See Specify file type for comparison manually.
• FontDirectories — provide custom font directories used while rendering the result. See Load custom fonts.

Once the basic comparison works, common follow-up tasks include:

• Customize changes styles — change highlight colours, fonts, and formatting.
• Adjusting comparison sensitivity — tune how granular the comparison should be.
• Get list of changes — retrieve detected differences as a structured collection.
• Work with the comparison result — use the returned result path and open the result with other libraries.
• Accept or reject detected changes — apply changes selectively.
• Compare multiple documents — compare more than two files in a single pass.
• Load password-protected documents — provide passwords for protected source or target files.