A week ago, on July the 16th,2019, I have sent my initial PhD proposal to a prospective supervisor in New Zealand who I have previously made direct contact with, after 4 days I sent another email to make sure he received my documents, but there was no response. I just want to make sure that he can open my file without difficulty. What am I supposed to do now?
You may want to wait a while (generally, I will suggest that you wait one week before contacting the prospective professor). Based on my experience, it will take some time for your prospective supervisor to read and comment on a research proposal, if he or she is reading it seriously, which is what you want. If he or she has any difficulty opening your file, he or she will let you know, so you do not need to check with him or her.
If there is no response after one week, you may want to remind him or her by sending an email but make sure you are being very, very, very polite about it.