When setting up a PDF Catalog, you need to select categories within the configuration that will take into account the products present in the selected categories.
However, it is not possible to select specific products. The workaround is to create a hidden category on your PrestaShop and add products to it.
You'll then be able to select this specific category within your PDF Catalog configuration, and the catalog will include products you would have added to that hidden category.
You can use our Store Commander module to make this task easy and fast, with a simple drag and drop :)
>> Check how on the article listed below.