Docotic.Pdf library can open PDF files of any version up to the latest published standard (PDF 1.7 for now).
You can add new content to existing PDFs, add text and images to existing pages, fill in forms, and otherwise update your files.
With the library you can optimize your PDFs created in other applications or by other libraries.
The library can compress images, optimize internal objects, replace duplicate fonts, flatten form form fields and remove structure information. Please look at Compress PDF document in .NET sample for more detail.