We provide the candidate image value in the 'CandidateImageData' tag for Word documents only, not for PDF files. So, you will not be able to get the candidate image data value for a PDF file.
Consequently, retrieving the candidate image data value for a PDF file is not possible.
Moreover, within the document, our parser performs face detection on all the images to extract the candidate images. If the candidate has mentioned multiple images, the image containing a face will be extracted as the candidate image. Images without a face, or those unrelated to the candidate, will not be extracted by the parser. Therefore, it is essential that the image includes a face in order to be considered as a candidate image.
Also please check your API Settings and make sure that HTML Format is enabled.
If you are parsing the doc/docx file and still not getting candidate image data, you can contact RChilli Support by creating a ticket at RChilli HelpDesk or sending an email at firstname.lastname@example.org. The Support Team will assist you further.