Even though you may start your presentation on time, you may have a few participants who arrive late for whatever reason: traffic, childcare issue, work issues, etc.

For the most part, late arrivals will normally quietly come in and find a seat without interrupting the presentation. Unless they have a specific question or need, greet them silently with a nod and/or smile, and continue with your presentation.

As suggested earlier, to minimize distractions, set up all participant materials on a table near the door so late arrivals can get what they need without having to interrupt you in the middle of your presentation.