Migrating from Outlook 2003

My old man used this Outlook for many years, but after an internet provider change, we prepared a gmail account for him, but Outlook 2003 doesn’t synchronize well with it.

We wanna try eM Client, but I wanna make sure that it will migrate the full pst backup, messages and folders. Is eM Client able to do this? Is there a guide?

Yes, eM Client can do this. Have a look at this page in the Help File:

eM Client | Documentation - Import from Microsoft Outlook