sample-process-models/misc/qa/forms/pdf-file-upload/pdf-file-upload-uischema.json

{
"invoice": {
"ui:order": []
},
"filesAccept": {
"ui:help": "Click here to select file to upload",
"ui:options": {
"accept": ".pdf"
}
},
"ui:order": [
"invoice",
"filesAccept"
]
}