In short: yes.
PDFs are generally not a terribly optimisable format – if you can have content in HTML format (a normal webpage) then you should. But sometimes content lends itself to PDFs; you may have products that have datasheets in that format on top of their product descriptions, or articles with images and particular formatting and borders, and in these cases sometimes PDFs need to stay as PDFs.
However, you can still work on these PDFs to ensure they are working for your digital marketing and not against it. Google does index PDF content (some PDFs are purely image, but most are in a format that allows the search engines to read the text), so all that remains is for you to ensure you use every available method to give Google clear instructions on what the PDF is about and how it relates to your overall marketing objectives.
Firstly, as with all other formats online (webpages, text documents etc) the file-name offers an excellent opportunity to tell the search engines exactly what this file is about. So rename your file, ensure it has no spaces in the file-name (this is another good practice that applies to all other online files too)and make it relevant, concise and descriptive.