For a client, I need to be able to read and write PDF files. There are two downsides to this:
Agree with the answers above. Implementing a PDF engine isn't a trivial task. If you need to do the full one reading and modifying PDF, then use third party library like suggested.
I have worked with PDF document creation, management and etc for several years. Often I found that the requirement to handle PDF can be very basic and achieved quite easily but misunderstood. I will just list some options here to consider if one of your requirement fall in to this category: