目前正在为父母网上办理续签，其他文件都以DOC格式成功上传，就是IMM5708这个PDF文件，已经填写好也VALIDATED 但是当我上传的时候总是提示如下内容：
Validation error: You have not completed the mandatory fields or you have not completed them correctly. Please make corrections where indicated.
Validation error: You have not completed the mandatory fields or you have not completed them correctly. Please make corrections where indicated.
- Error Description:
Document is not a valid PDF file
