If you created your 2017 tax return and printed it but never mailed it in to the IRS (I am also assuming that you did not e-file it, either), then you can still mail the 2017 return now to the IRS (in fact, it's a very good idea).
If, however, you e-filed the 2017 return last year, then you do not need to mail the printed copy of the 2017 return to the IRS.
If you owed the IRS money from the 2017 return, you should include a check for the amount showing as tax due on the return when you mail it to the IRS. However, don't be surprised if you receive a letter from the IRS sometime later asking you to pay penalties and/or interest on the amount owed and not paid on time.
If you were due a refund, the next notice from the IRS will likely be a direct deposit or a refund check.
If you created your 2017 tax return and printed it but never mailed it in to the IRS (I am also assuming that you did not e-file it, either), then you can still mail the 2017 return now to the IRS (in fact, it's a very good idea).
If, however, you e-filed the 2017 return last year, then you do not need to mail the printed copy of the 2017 return to the IRS.
If you owed the IRS money from the 2017 return, you should include a check for the amount showing as tax due on the return when you mail it to the IRS. However, don't be surprised if you receive a letter from the IRS sometime later asking you to pay penalties and/or interest on the amount owed and not paid on time.
If you were due a refund, the next notice from the IRS will likely be a direct deposit or a refund check.