You can just use the allow additions property to stop the form from adding new entries.

Is this just a one to one relationship? If so just turn off the navigation bar on the sub form, make sure the child/parent property is set correctly in the properties of the sub form, and set the default value of the ID field in the subform to equal your parent forms ID that links them.

Hi David,
Adam is correct. If you have a true subform it will be linked to the parent form. If ,in design mode, you click on the very outside line on your subform and then go to properties you will see LinkMasterFields and LinkChildFields. Each one should have the linking field. That is how the relation is established. As Adam said, in Design mode, simply click on the small square on the upper left of your form, go to properties and you will see (allow additions, allow deletions, allow edits, allow filters) If you want to turn any of those off simply click on or more.
HTH
John

Hi Adam, John. Thanks for the info. I actually had my settings correct but I was accidentally developing my DB file on OneDrive instead of my local computer, which caused my errors.

LOL! I am only human!