Today, we will provide password protection to our presentation files programmatically. In this article, we will see how to lock PowerPoint presentation files with password protection in C#. Further, we will learn to unlock these by removing the password and also how to change the existing password of PPT & PPTX presentation files. 本文讨论了以下主题：
Let us learn to secure our documents from unauthorized access. Previously we discussed [adding text and image watermarks to the documents][1] to avoid and illegal use. In this article, we will see how to add password protection to PDF documents to get them locked using C#. Additionally, we will change the existing password and also learn to remove the password to make the PDF unlocked. 本文讨论了以下主题：
To combine the data that is present in multiple documents, and sometimes in documents of different file types, there comes the need to merge all your documents or the portion of the documents into one. In this article, you will learn, how to merge multiple documents of either the same or different file types in one file using C#. 以下是本文涵盖的主题：