You can include contacts from other accounts in the Contacts app > Passwords & Accounts > Add Account.
Choose an account, sign in to it, then turn on Contacts.
Go to Settings Sync iPad with your computer.
If you use iCloud for Contacts, your contacts are kept up to date automatically, and no options appear for syncing them with your computer.
Tap a .vcf attachment in an email or message.
Tap Groups, then tap the GAL, CardDAV, or LDAP directory you want to search.
Tap Done, then enter your search.
Tap the person’s name to save their info to your contacts.
Tap Groups, then select the groups you want to see.
This button appears only if you have more than one source of contacts.