placeholder image not working

Hi I have created an interactive form in InDesign and saved as an interactive pdf with fields for text and image placeholders which allow the user to upload an image - it all works fine on my computer but the upload image functionality is not working for my client - I have saved it as 'Save as other .. reader extended pdf etc. but at a loss to know what else to try - is there an issue with computers with outdated software? Anything I'm missing?