Spending BTC from an Electrum watch-only paper wallet?
As you know, it isn't possible to spend money using a wallet that doesn't contain the relevant private-key. Your watch-only wallet cannot be used for spending.
See https://bitcoinelectrum.com/importing-your-private-keys-into-electrum/
In brief it says

These instructions are for Electrum 3.0 and later.
You cannot import private keys into an existing HD wallet.
Start new electrum wallet file
Click on next to see the wallet type selection window:
select “Import bitcoin addresses or private keys”.
Enter one private key per line. Electrum supports mini private keys and full sized keys in Wallet Import Format (WIF).

You may need to convert your BIP-38 data into WIF first.
It is worth reading their notes on why you might prefer sweeping to importing despite the transaction fees involved.