Although there is no special command to add a frame to an entire slide, there are several ways you can do this. One way is to create a frame with the outline of a shape. The second option is to use the Bing image search feature built into PowerPoint to find and insert a frame. Let's see how it's done.
Adding an edge to a slide using a shape outline
Open your presentation and select the slide to which you want to add a frame.
Go to the Insert tab, and then click the Shapes button. Choose a shape from the category Rectangles. In this example, we use a simple rectangle with square edges.
A crosshair icon is displayed. Position the crosshairs with the mouse in the upper left corner of the slide.
Press and drag your mouse to draw a rectangle shape that spans the entire slide. Release the mouse button to stop drawing. If you do not get the positioning right the first time, you can grab and drag one of the handles on the shape to resize it.
Now you have the size of the border right, you want to remove the background color from the shape. On the Format tab, click the Shape Fill button, and then click the No Fill command from the drop-down menu.
By default, your rectangle shape has a thin border, but you can make it thicker if you want. On the Format tab, click the Shape Outline button. In the drop-down menu that appears, point to Weight, and then choose a thickness for your frame. In this example, we go with a thickness of 6 pt. The result is a thick border around your slide.
Do you want an even denser border? From the Shape Outline drop-down menu, click the More Lines command to open the Format Shape area. In the "Line" section of this area, you can adjust the Width setting by entering a point size or by clicking the up and down arrows. In this example we have increased the width to 20 pt.
To add the border to additional slides, select your shape and then click the "Copy" button on the Home tab (or just press Ctrl + C). Switch to another slide and then click the "Paste" button (or press Ctrl + V).
Finding a Frame Using Bing Image Search
Instead of adding a simple border for a border, you can also search for a bordered border image. Select the slide to which you want to add a frame, go to the Insert tab, and then click the Online Images button.
Enter a search phrase, z Click a frame you like, and then click Paste to add it to your slide. Click "Search" (or press Enter)
We have a little bonus tip for you. If you use a background image on your slide and it's a white border, you do not even need to add a border. You can resize your wallpaper to be slightly smaller than your slide. This creates the illusion that your slides have a white border. Have a look: