A company when sets for digital marketing, it has to cover many of it's aspects for not only being on the top result pages but also in top ads. It matters a lot when your company is found on top in ad areas of search engines.
There are two parts of Digital marketing and they are paid and organic (only pay for the SEO service). The search engine optimization part totally depends upon the on-page and off-page techniques of SEO, which is free of cost. You need to pay for SEO only when you are hiring some company to do it for you.
PPC services come under paid category and you need to pay for your ads to companies showing them, when they are clicked by a person. It is nothing but search engine marketing (SEM), a big term after SEO.
SEO: You can get first page positions if your web site is optimized for search engines. Organic traffic is continuous given that you are ranking in one of the top positions.
PPC: You can get more clicks for your ad on the first page by paying a higher cost per click.
SEO: A bit cheaper.
PPC: Compared to SEO, PPC is costlier but more effective in terms of conversion.
The bottom line is, PPC can bring you faster results so you can run a PPC campaign and test which keywords convert better and then try with SEO to rank for those keywords on SERP(Search Engine Result Pages).
Read our related article on How To Choose Best PPC Advertising Services Company?