com.aspose.words

Example:

Document doc = new Document(getMyDir() + "Rendering.docx");

HtmlFixedSaveOptions htmlFixedSaveOptions = new HtmlFixedSaveOptions();
{
    htmlFixedSaveOptions.setPageHorizontalAlignment(pageHorizontalAlignment);
}

doc.save(getArtifactsDir() + "HtmlFixedSaveOptions.HorizontalAlignment.html", htmlFixedSaveOptions);

String outDocContents = FileUtils.readFileToString(new File(getArtifactsDir() + "HtmlFixedSaveOptions.HorizontalAlignment/styles.css"), StandardCharsets.UTF_8);

switch (pageHorizontalAlignment)
{
    case HtmlFixedPageHorizontalAlignment.CENTER:
        Assert.assertTrue(Pattern.compile(
            "[.]awpage [{] position:relative; border:solid 1pt black; margin:10pt auto 10pt auto; overflow:hidden; [}]").matcher(outDocContents).find());
        break;
    case HtmlFixedPageHorizontalAlignment.LEFT:
        Assert.assertTrue(Pattern.compile(
            "[.]awpage [{] position:relative; border:solid 1pt black; margin:10pt auto 10pt 10pt; overflow:hidden; [}]").matcher(outDocContents).find());
        break;
    case HtmlFixedPageHorizontalAlignment.RIGHT:
        Assert.assertTrue(Pattern.compile(
            "[.]awpage [{] position:relative; border:solid 1pt black; margin:10pt 10pt 10pt auto; overflow:hidden; [}]").matcher(outDocContents).find());
        break;
}