iText是一個支持創(chuàng)建和操作PDF文檔的PDF庫，通過動態(tài)生成和操作PDF文檔，iText能幫助開發(fā)者進一步提升網(wǎng)站和應(yīng)用程序的性能，它也同時支持Java和C#。

創(chuàng)建PDF

有了Document和PdfWriter類，你可以從數(shù)據(jù)庫，XML文件或者其他數(shù)據(jù)源開始創(chuàng)建PDF文檔，可以通過以下三種途徑完成：

• 使用高層次的對象，如Chunk、Phrase、Paragraph、List等等。這些對象通常被稱為iText的基礎(chǔ)構(gòu)造模塊。
• 使用低層次的功能。這是通過PdfContentByte類完成的，它包含了一系列方法，可以映射到Adobe成像模型中的每一個操作員和運算對象。這個類還包含大量便捷的方法，用以繪制絕對定位的圓弧，圓和矩形。
• 使用PdfGraphics2D類，它是iText對抽象類Graphics2D的實現(xiàn)（不適用于iTextSharp）。
  

iText附帶了大量類，可支持ecnryption、不同的圖像類型、色彩空間和字體，增強PDF文件的可訪問性，支持Flash應(yīng)用程序集成到PDF中等。

iText可以將XML或者XHTML/CSS文件轉(zhuǎn)換為PDF文件（使用XML Worker）。iText不支持將文件從一種格式轉(zhuǎn)換為另一種格式，不支持將Word文檔轉(zhuǎn)換為PDF文檔。

更新PDF

當你需要一個PDF閱讀器來訪問現(xiàn)有的PDF文檔，你可以使用這個閱讀器，結(jié)合PdfStamper標記當前PDF文檔中額外的內(nèi)容，如頁碼、水印和注釋等等。PdfStamper類還支持填寫交互表單。

你也可以通過PdfCopy，PdfSmartCopy，PdfCopyFields，甚至使用結(jié)合PdfWriter或PdfStamper的PdfImportedPage類來拆分和合并PDF文檔。iText不支持將PDF文檔轉(zhuǎn)換為另外格式的文檔，但是如果PDF文檔被標記或者包含結(jié)構(gòu)樹，你可以將它轉(zhuǎn)換為XML文件。

iText還可以對現(xiàn)有的PDF文檔進行簽名和加密。

閱讀PDF

iText不是PDF查看器，不能將PDF轉(zhuǎn)換為圖像，也不能打印PDF文檔，但是PdfReader能讓你訪問一些特定類，這些類創(chuàng)建PDF文檔和頁面中的內(nèi)容流。內(nèi)容流能被解析，并且如果它們不是以柵格化的文本添加到頁面中的，你可以將頁面轉(zhuǎn)換為純文本。同時，iText不支持OCR。

何時使用iText

一般情況下，iText適用于有以下需求的項目中：

• 內(nèi)容無法提前利用：取決于用戶的輸入或?qū)崟r的數(shù)據(jù)庫信息。
• 由于內(nèi)容，頁面過多，PDF文檔不能手動生成。
• 文檔需在無人參與，批處理模式下自動創(chuàng)建。
• 內(nèi)容被定制或個性化；例如，終端客戶的名字需要標記在大量的頁面上。

Creating PDFS

With the Document and the PdfWriter class, you can create PDF documents from scratch from a database, an XML file, or any other data source. You can do this in three different ways:

• using high-level objects such as Chunk, Phrase, Paragraph, List, and so on. These objects are often referred to as iText's basic building blocks.
• using low-level functionality. This is done with PdfContentByte, a class that consists of a series of methods that map to every operator and operand available in Adobe's imaging model. This class also has numerous convenience methods to draw arcs, circles, rectangles and text at absolute positions.
• Using PdfGraphics2D which is iText's implementation of the abstract Graphics2D class in Java (not available in iTextSharp).

iText ships with a plethora of classes that support ecnryption, different image types, color spaces, fonts. There's functionality to enhance the accessibility of the PDF file, support for the integration of Flash apps into the PDF, and so on.

iText can convert an XML or an XHTML/CSS file to PDF (using XML Worker). Converting documents from one format to another is outside the scope of iText. And no: iText does not convert Word documents to PDF!

Updating PDFS

You always need a PdfReader instance to access an existing document. You can use this reader in combination with PdfStamper to stamp extra content on the existing PDF document: page numbers, a watermark, annotations, and so on. PdfStamper is also the class you'll use to fill out interactive forms. iText has almost complete support for AcroForms, but as soon as you have a form involving the XML Forms Architecture, the possibilities are limited.

You can split and merge PDF documents with PdfCopy, PdfSmartCopy, PdfCopyFields, and even using PdfImportedPage objects in combination with PdfWriter or PdfStamper.
Converting a PDF document to another format is outside the scope of iText, but you can convert a PDF to XML if the PDF was tagged and contains a structure tree. Depending on how the PDF was created, you can also extract plain text from a page.

iText can also be used to sign existing PDF documents, as well as to encrypt them.

Reading PDFS

iText isn't a PDF viewer, iText can't convert PDF to an image, nor can iText be used to print a PDF, but the PdfReader class can give you access to the objects that form a PDF document and to the the content stream of each page. This content stream can be parsed and if the content wasn't added as rasterized text, you can convert a page to plain text. Note that iText doesn't do OCR.

When to use iText?

Typically, iText is used in projects that have one of the following requirements:

• The content isn't available in advance: it's calculated based on user input or real-time database information.
• The PDF files can't be produced manually due to the massive volume of content: a large number of pages or documents.
• Documents need to be created in unattended mode, in a batch process.
• The content needs to be customized or personalized; for instance, the name of the end user has to be stamped on a number of pages.