With the pdf reader from the marketplace you can extract the content of the pdf file. Then use google translate or AWS translate connector from the market place e.g. to get the translated version of your text. The text could then be store in an entity and with a document template you can create a new pdf. With some microflow logic replace the original file with the translated version.

Layout could be an issue here though, but at least this gives you some idea on how to proceed.

Another option could be to find a translation service with an API to perform the work for your app.