Blenders and food processors serve similar purposes, but they're often used in very different ways. It's a good idea to have one of each in your kitchen, but if that's not possible, they can be used almost interchangeably for many tasks. If you only have a blender, you can adjust the way you use it to achieve a similar effect to what a food processor does.
Slow Down the Blending Process
Blenders typically work at a higher speed than most food processors, which might leave whatever you're trying to create much smoother than you want it to be. To simulate the power of a food processor, pulse the blender instead of letting it blend for an extended amount of time.
Avoid the "Liquefy" and "Purée" Settings
Blenders are typically used for making liquid drinks, chopping ice, or puréeing soups, whereas food processors are mainly used to chop and combine.
Use Less Liquid
Go easy on the liquid, at least initially. This helps to replicate the effect of using a food processor without making your food too soupy. As you're blending, you can always add more liquid for a smoother result.