Thank you for considering Aspose products.
Currently, Aspose.OCR components (both flavors) can only process images to perform OCR on them. Ability to load PDF files is not supported at the moment. Although you can use a combination of Aspose.OCR for Java and Aspose.PDF for Java in order to achieve your goals. For instance, you can convert a PDF file to image using Aspose.PDF for Java, and extract text from the image using Aspose.OCR for Java API.
Please feel free to write back in case you face any difficulties.