Two very different things get called opening an iPhone backup, and the difference decides whether anything on your PC or phone changes.
Restoring is a phone operation. When Apple Devices or iTunes restores a backup, it writes the backed-up data onto an iPhone in place of what that phone holds. It exists for setting up a replacement phone or putting a phone back as it was, and it is all or nothing: there is no way to restore a single conversation. Reading old texts this way needs a spare phone you are willing to overwrite.
Viewing is a PC operation. A viewer reads the backup folder where it is and shows you what is inside. Nothing is sent to a phone, and nothing in the backup should change. BackupPaper opens the folder read-only and refuses to save an export into the backup folder, so the backup you close is the backup you opened.
What BackupPaper shows, and what it leaves out. It reads the Messages app: iMessage and SMS conversations, group conversations included. Each message appears with its time, sender, text, reactions, replies and attachment names. Photos, videos, notes and other app data are not shown, and WhatsApp, Signal and other chat apps are not read. Treat it as a viewer for the Messages part of a backup, with an export button.
Which folder to choose. Apple Devices and iTunes from the Microsoft Store keep backups in %USERPROFILE%\Apple\MobileSync\Backup. iTunes downloaded from Apple's website uses %APPDATA%\Apple Computer\MobileSync\Backup. Inside, each backup is its own folder with a long coded name; choose that folder itself, not the Backup folder above it. BackupPaper shows the device name and backup date after it opens a folder, so if there are several you can check them in turn. The next time you start it, it reopens the last backup.
When the list comes up empty. Apple says a backup made on a computer leaves out iMessages and texts that already sync to iCloud. If Messages in iCloud was on, the backup may hold few or no conversations, and BackupPaper will tell you the backup has no conversations. No viewer can show messages that were never written into the backup, and BackupPaper does not bring back deleted messages either. The 15-day free trial is the practical way to find out what a particular backup holds.
Encrypted backups. If Encrypt local backup was on, BackupPaper asks for the password you set in Apple Devices or iTunes. The password is used on this PC and is not saved. On our test PC, checking it took about five seconds. Without the password the backup stays closed; BackupPaper cannot recover or reset it.