After made iText worked on Google App Engine, I built Another application, Remove PDF Password Online. It bases on iText 2.1.7 but with many modification.

the main features of pdfdecrypt online are,

• remove restrictions on any secured PDF document (you should have the right to do it, for example, if you forgot the password). Any Acrobat version up to 9 is supported, even with 128-bit AES or 128-bit RC4 encryption. PDF restrictions removal is an instant process. Unlocked file can be opened in any PDF viewer without any restrictions so you may edit/copy/print it.
• remove the PDF open password. Decryption of the file with password for opening is guaranteed for PDF files Any Acrobat version up to 9 is supported, even with 128-bit AES or 128-bit RC4 encryption,but you must know the password first.

It supports upload PDF documents from your disk and give a PDF url.

If you like it, just have a try now, it is free.

A digital signature is like a paper-based signature – each giving you a method for adding a unique identifier to a document. Both provide you with an easy way to show a person signed a particular document at a particular time, but a digital signature goes further as it can ensure that the document content has not been tampered with after it was signed. In addition, the document version history can let recipients see when a document was signed and see when any changes were made to it. This revision history is encrypted and stored inside the PDF and can be viewed at anytime via the Signatures pane.

To digitally sign a PDF document, you must have a digital ID, and to verify other people’s signatures, you must first share your digital IDs and add each other to your Trusted Contacts list.

Most Digital Signature software are not free, but I will introduce you some free software developed in JAVA and DOTNET with the power of iText and iTextSharp.

• PDF Digital Signer, it is portable version developed by RubyPDF
• jPDF Tweak, java version, Open Source.
• JSignPdf, Java version, Open Source.

Want to develop your own? please visit How to sign a PDF using iText and iTextSharp.

Here is a Windows command line version PdfSigner with TimeStamp(TSA) support,

Usage pdfsigner InPdf OutPdf Pkcs12KeyStore Pkcs12KeyStorePassword

because It is a demo application, so the TSA server only supports http://tss.pki.gva.es:8318/tsa
If you have interest, please download it here,pdfsigner(4.9M)