You can predefine design templates for your slides on Slide Masters and Layouts. You do not have to utilize PowerPoint's slide masters and layouts to generate an accessible PDF document from your presentation. However, it can make it easier for you to work on a consistently designed presentation.
Recommendations on how to format your texts for accessibility can be found in Text Formatting.
Editing Slide Masters and Layouts
To open the slide master, select the View tab in the ribbon and click on the Slide Master button. The Slide Master tab shows up in the ribbon.
You can recognize the slide masters by the prefixed slide number in the navigation bar. Several layouts can be assigned to each slide master. Placeholders for titles, texts, and other objects such as graphics are placed on the slide master and the layouts.
For example, you can format the appearance of the slide titles and text levels on a Slide Master. All changes you make to the slide master also change the subordinate layouts.
You can use Layouts to create individual design templates for your slides. You can insert various placeholders for texts and objects such as graphics, diagrams, and tables.
Important: Make sure that there is a placeholder for the title on your layouts. Slide titles are important for accessible navigation. You can find out more about this in Slide Titles.
To exit the Slide Master View and return to your presentation, select the Slide Master tab in the ribbon and click on the Close Master View button.
Using Layouts
To insert a new slide with a specific layout, select the Home tab in the ribbon and click on the New Slide button in the Slides function group. There you can select a layout template.
To change the layout of an existing slide, select the Home tab in the ribbon and click on the Layout button in the Slides function group. Select the desired template in the menu that opens. It is best not to use the "Blank" layout template, as this does not have a placeholder for the slide title.
Important for the PDF Export With axesSlide
The slide masters and layouts are for design purposes only and no information relevant to the content should be inserted there. Insert important content-related information that all users should have access to directly on your slides or repeat it there. When exporting PDFs with axesSlide, all objects such as graphics, background images, text, etc. that are inserted on the slide master or layouts are automatically marked as artifact (i.e. marked as decorative). Assistive Technologies then do not read these objects. As the objects may be repeated on several slides, they would disrupt the reading flow.