You can import contacts saved in vCard format (.vcf, .vcard) directly to Contacts (known as Address Book before Mountain Lion) and save them to the existing database, which is the .abcddb file. So no conversion needed, just import of contacts.
Convert vCard contacts to Apple Address Book database.
We have found one software suitable in our database for this conversion.
Apple macOS / Mac OS X software - convert vcf to abcddb on OS X
Contact management tool for Mac OS X
Convert from vcf file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.