The most direct and honest method is sending a friend request. Include a polite message explaining who you are if you do not know them well.

Software promising a "full download" of a private profile is typically a vector for malicious activity. Data Harvesting (Phishing)

Downloading software claiming to be a "full" Facebook private profile viewer is highly dangerous and largely ineffective. Most tools that promise to bypass Facebook’s server-side privacy controls are phishing scams or malware designed to steal your credentials or personal data. Google Play The Reality of "Private Viewer" Software Technically Impossible

Is there a facebook private account viewer that actually works?

Since you’re searching for ways to view others’ private info, you might also want to ensure your own profile stays locked down. Here’s how:

Searching for a "full download" of hacking or viewing tools puts your own digital safety at extreme risk. Most of these files are "Trojan Horses"—malicious software disguised as a helpful utility.