If you have created a PDF file and are distributing it over the internet, then you should watermark it before putting it online so that anyone who downloads the PDF file knows about the owner or the source of the file. Another way to secure a PDF file and tell people where it came from is by digitally signing the PDF file. And if the PDF file is meant only for a few individuals or it contains some sensitive private matter then you should encrypt it first so that only the intended parties can access it.
For encrypting, watermarking and digitally signing your PDF files, you can use a software called Secure-PDF. This software has a very easy to use interface from where you can select one of the operations – encrypt, sign, watermark or ownership information. Based on the operation selected, you will be taken to a different window from where you can choose operation specific settings. For example, if you choose to watermark your PDF document, you have to first select a PDF file and then choose a PNG image containing the watermark. In case of digitally signing the PDF document, you have to give all the details like digital signature file, username, password and the signature image file.
Secure-PDF uses very strong AES-256 it cipher for encrypting your documents which makes it virtually impossible to break the encryption and decrypt the encrypted PDF without the correct password. For digitally signing the documents, you have to obtain a PKCS#12 certificate (also called P12 or PFS). Alternatively, you can just put the image of your scanned signature on the PDF document but there is no way to validate this signature compared to a digital signature obtained from a well known certification authority such as DigiCert.
All in all, Secure-PDF is a very useful application for quickly securing your PDF documents. It provides various methods of ensuring that your PDF files are not tempered with or at the least are watermarked.
You can download Secure PDF from https://www.ascomp.de/en/.