Do you actually have a backup of the texts? If so, what is the file/folder called?
If you ran a message backup app, then copied the backup to the PC, then how you read the texts will depend on the format of the backup, which depends on what app you used. If you had not backed the texts up on the phone, and simply copied everything you could see via Windows Explorer then it's unlikely that you have a copy of the texts at all.
Messages are stored in a database file, /data/data/com.android.providers.telephony/databases/mmssms.db. But the /data area isn't browsable unless you have root privileges, and shouldn't be visible to Windows Explorer. Hence if all you did was just copy everything that Windows Explorer could see it's very unlikely you have a copy of your messages, unless, as noted above, something else had already backed them up to the part of the internal storage that Windows Explorer can see.