Yes, you can, but you probably shouldn't. Importing an external @blockchain is very resource intensive and forces you to trust the entity providing you with the blockchain. It's usually faster to download it the normal way: running a node and letting it synchronize with the other @nodes in the network. If you really need to import an external blockchain, you can download one in the 'Downloads' page of this website. Follow the guide below if you are using Windows. If you are a linux user, you can use the tool "monero-blockchain-import", which is included in the archive when you download the GUI or CLI wallets. Start syncing the imported blockchain with this command: "monero-blockchain-import --input-file blockchain.raw".
