@ApiModel(value = "Document information")
public class DocumentDto {

public enum DocumentType {
    PDF,
    WORD,
    CSV
}

.........

@NotNull
@ApiModelProperty(required = true, value = "document type", allowableValues = "PDF, WORD, CSV")
private DocumentType documentType;

........

@JsonIgnore

@ApiOperation(value = "is this document a PDF?")
public boolean isPDF() {
    return documentType == DocumentType.PDF;
}