Understanding the Portable Document Format PDF. Preface I wish to acknowledge that this article was written with full reference tohttp www. Daemon_Tools_Lite_4_images_screen_thumb_large650_450.png' alt='Apache Pdfbox Pdf To Html' title='Apache Pdfbox Pdf To Html' />PDF3. Most of all that I have learned about PDFs are from the above reference. If you are really interested take time to read it. Surprisingly, it is easy and interesting to readI am writing this tutorial out. PDF specification. My. quest started when I tried hard but failed to extract text from a simple PDF. Please let me know steveprintmyfolders. I have relied on the PDF specification link on page top to create this tutorial. This tutorial covers PDF files conforming to the ISO 3. Pages vi to viii in the PDF3. PDF files are interesting. If you were to open a PDF file in a text editor like Notepad, the contents may look like junk and probably not very interesting. But it will make a little more sense once you understand that PDF files follow a set pattern. At the core of PDF is an advanced imaging model derived from the Post. Script page description language. This PDF Imaging Model enables the description of text and graphics in a device independent and resolution independent manner. To improve performance for interactive viewing, PDF defines a more structured format than that used by most Post. Script language programs. Apache Pdfbox Pdf To Html' title='Apache Pdfbox Pdf To Html' />PDFBox Tutorial, PDF Specification PrintMyFolders Software. Whitespace characters Null, Horizontal tab, Line feed, Form feed, Carriage return and Space. Recently I had to extract text from PDF files for indexing the content using Apache Lucene. Apache PDFBox was the obvious choice for the java library to be used. Hi, Thank you for a very helpful article. Being able to easily extract highlighted text from a pdf in the form of a summary would be a huge timesaver. Free SAP Hybris, FlexBox, Axure RP, OpenShift, Apache Bench, qTest, TestLodge, Power BI, Jython, Financial Accounting, text and video tutorials for UPSC, IAS, PCS. Unlike Postscript, which is a programming language, PDF is based on a structured binary file format that is optimized for high performance in interactive viewing. PDF also includes objects, such as annotations and hypertext links, that are not part of the page content itself but are useful for interactive viewing and document interchange. Quoted from Page vii of PDF3. The basic building blocks of a PDF files are objects. There are eight types of objects that are used in PDF files. Before we look at them we will briefly look at the character set of PDFs. There are 3 types of characters white space, delimiter and regular characters. White space characters Null, Horizontal tab, Line feed, Form feed, Carriage return and Space. Tip If you need to remember them, imagine seeing them in sequence except for null of course being typed on an imaginary typewriter. White space characters separate names and other objects from each other. Interestingly, PDF treats all white space characters outside a comment, string or stream the same. Outside a comment, string or stream, PDF considers any sequence of consecutive white space characters as one character. What this means is that you may have 5 spaces but in reality it is considered as one. Note that this does not apply to white space characters within strings, streams and comments. The Carriage return and Line feed are considered as end of line EOL markers. EOL markers play a very important role in showing where a new line starts. Carriage return followed immediately by a Line feed is considered as one EOL marker. Delimiter characters, lt, and 4 pairs and 2 unique. These are used in the objects we would look at later. They basically act as delimiters mark the boundary or border for entities. Tip If you need to remember them, imagine these characters being bent lt and then stretched and then bent again and then eventually made flat. Regular characters All characters other than White space and Delimiter characters including those that are not part of the standard ASCII character set. Please read the note below as it is critical you understand this. An interesting fact to note is that a PDF may consist entirely of just ASCII characters or can consist of ASCII characters and Binary data. In simple terms, characters in ASCII files use only 7 out of the 8 bits in a byte while characters in the Binary files use all the 8 bits in the byte. This allows a possibility of 1. ASCII files and 2. Binary files. Most PDF files that are encrypted or contain images will have binary data images are represented in binary. PDF files that contain binary data get corrupted when edited or even opened and saved in normal text editors like Notepad. It is critical that we understand the difference between ASCII and Binary files as other areas of the PDF specification touch on them. Here is an interesting link that explains the difference between Binary and ASCII files. NotesBit. Opascii. Bin. html You may also wonder why you dont see any text that can be seen when opened using a reader or its equivalent when opening a PDF file in a text editor or even binary editor. There may be two reasons. The first and most common reason is that the content stream where the text is storedkept is encoded transformedchanged to conserve space. This is what happens with most files. The second reason could be that the PDF file is encrypted purposely to keep the text secure. Here are the objects that make use of the characters we looked at above. Boolean objects The keywords true and false. Numeric objects There are two types integer real. Integers are numbers. For. instance, the number 1. Real numbers must have a decimal point. For instance, 1. 0. Real numbers cannot be expressed in exponential format. String Objects Strings contain characters can be zero characters as well. They can be literal characters within parenthesis or hexadecimal data within. Notice that the parenthesis and angle brackets are delimiter characters. There are escape characters that can be used. Refer to. the PDF specification for more details. The sequence ddd where ddd is an octal character code can be used to represent characters outside the printable ASCII character set. Be aware that, some of the escape characters, especially the ones that cause characters to move, for instance n newline, did not have any visual effects when I added them to a string displayed by the PDF. You can replace one of the characters in the string I have used in the sample PDF and notice no difference. We can also use octal characters usually to represent character outside the printable ASCII character set when using parenthesis. An octal character is represented in the format ddd. In the following example 0. ASCII character. I love Java and 0. PDFHere is an example of a String represented with hexadecimal numbers. Each pair is taken as a value. In the above example, the hexadecimal value. ASCII equivalent of H. Likewise 4. 5 is E, 4. C is L and 4. F is O. The above string is same as the string HELLO. If the final hexadecimal digit is on its own without another digit to make a pair a zero. Name Objects Names consist of a sequence of characters except null. A. forward slash must be used to introduce the name. In case hash is part of the. To represent characters using. All characters. that are not regular characters have to be represented by the followed by. Please refer to the PDF specification for more details. Vengeance Producer Suite Download on this page. My2. Name represents My Name. All2. 02. 3Numbers represents All Numbers. Array Objects These are similar to the arrays found in computer languages but differ in that they can contain different object types including strings, names. Arrays are represented within square brackets. As you can see, the values are separated by spaces. Hello My2. 0NameArrays are single dimensional but can include other arrays. These are similar to an actual dictionary, where a description follows a word. The description here can be any object including. Name object that we just. The key Name is unique there cannot be two similar Names.