You have many tests - that is good.

The tests are running slowly - that is bad.

Maybe it's because the PDF documents are very large, but after all it has to be tested. Instantiate the test document only once for all tests in a class.

public class CachedDocumentTestDemo {

  private static DocumentValidator document;

  @BeforeClass  // Document will be instantiated once for all tests:
  public static void loadTestDocument() throws Exception {
    String filename = "documentUnderTest.pdf";
    document = AssertThat.document(filename);
  }
  
  @Test
  public void test1() throws Exception {
    document.hasNumberOfBookmarks(4);
  }
  
  // ... and more tests.

}

Of course, you can concatenate all test methods in one statement. But how would you name the test? Names of test methods should reflect the content as exactly as possible. Otherwise, a test report with many hundreds of tests is difficult to understand. So, testAll is a bad name - it means nothing.

PDFUnit is stateless. But it can not be guaranteed that 3rd-party libraries are also stateless. So, if you have problems with tests using cached documents, change the annotation @BeforeClass into @Before, remove the modifier static and the PDF document is instantiated for each test method:

@Before  // Document will be instantiated for each test. No caching:
public void loadTestDocument() throws Exception {
  String filename = "documentUnderTest.pdf";
  document = AssertThat.document(filename);
}