Using the versatile online tool "I Love PDF" is problematic when it comes to adding watermarks to PDF documents. Despite its numerous features and user-friendliness, integrating a watermark seems to be an issue. The difficulty lies in the fact that the watermarks are not properly placed or not placed at all on the PDF document. As a result, I can't see the watermark on my PDF files, which is problematic since this is an essential element to customize and protect my PDF documents. This challenge raises questions about how to solve such problems that the tool should actually be able to handle.

First, you should make sure you're using the latest version of "I Love PDF" since outdated versions might not properly support features like adding watermarks. Once you've logged in, select the "Add Watermark" option and upload your PDF document. In the next step, you can choose an image or text as a watermark and place it in your desired position. Pay attention to transparency and size settings so that the watermark is clearly visible but does not overlay the document's content. After making all the adjustments, click on "Add Watermark" to complete the process and download your new PDF with a watermark added.