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What Pdf Means?

Portable Document Format PDF is an abbreviation that stands for Portable Document Format. It's a versatile file format created by Adobe that gives people an easy, reliable way to present and exchange documents - regardless of the software, hardware, or operating systems being used by anyone who views the document.
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How are images stored?

When I was learning the PDF file format, I found Images could be quite a complex topic in PDF so I wrote this article to hopefully explain them clearly. Please do let me know if you have any suggestions to improve it or it raises any questions for you.

A PDF file usually stores an image as a separate object (an XObject) which contains the raw binary data for the image. These are all listed in the Resources object for the page or the file and each has a name (ie Im1). It is wrong to think of images embedded inside a PDF as Tif, Gif, Bmp, Jpeg or Png. They are not.

It is important to appreciate that this is not usually an image in the sense of a Tif or a Jpg or a Png image – it is the binary data for the pixels, the colorspace used for the image, information about the Image. The image is ripped apart when the PDF is created and different PDF creation tools may store the same image in very different ways.

Here is an example shown in the PDF object viewer in Acrobat 9

Sometimes the raw image data is adjusted to the required size needed for the page and sometimes it is not – in that case it is scaled up or down when it is drawn – different PDF creation tools create PDF files in very different ways.

The actual pixel data can be compressed and one of the compression formats (DCTDecode) is the same used as in a JPEG (JPX is the same as Jpeg2000). If you save this data, it can be opened as a JPEG file, but it may need altering to include the colorspace data.

This image is then drawn in the PDF contents stream by a DO command and the image name (ie Im1). The image can be used multiple times and scaled, rotated or clipped – it takes whatever vales are set when the DO command is executed. Some things which appear as an image to the eye may also be made up of multiple images or not even images at all!

All this means that if you want to extract images from a PDF, you need to assemble the image from all the raw data – it is not stored as a complete image file you can just rip out.

And also there is a ‘raw’ (which is sometimes a much higher quality and sometimes exactly the same size) version of the image and a clipped/scaled version of the image – both can be extracted (and you can also scale the clip up onto the raw to produce a higher quality image – see this PDF Clipped Image Extraction example).

As with everything PDF, there is a lot of flexibility and lots of alternatives and options…

This post is part of our “Understanding the PDF File Format” series. In each article, we aim to take a specific PDF feature and explain it in simple terms. If you wish to learn more about PDF, we have 13 years worth of PDF knowledge and tips, so click here to visit our series index!

8 Related questions Answers found

What does PDF data look like?

File format. A PDF file contains 7-bit ASCII characters, except for certain elements that may have binary content. The file starts with a header containing a magic number (as a readable string) and the version of the format, for example %PDF-1.7 . The format is a subset of a COS ("Carousel" Object Structure) format.

Can my phone read a PDF to me?

Open and read PDFs on Android. Download and install Acrobat Reader from the Google Play Store. Launch the app. On the bottom menu bar, select Files. Locate your PDF file on your Android and select it.

Where is PDF on my phone?

Navigate to the file manager on your Android device and find a PDF file. Any apps that can open PDFs will appear as choices. Simply select one of the apps and the PDF will open.

Is a PDF a photo?

A PDF file usually stores an image as a separate object (an XObject) which contains the raw binary data for the image. These are all listed in the Resources object for the page or the file and each has a name (ie Im1). It is wrong to think of images embedded inside a PDF as Tif, Gif, Bmp, Jpeg or Png.

What are PDF used for?

PDF, or Portable Document Format, is an open file format used for exchanging electronic documents. Documents, forms, images, and web pages encoded in PDF can be correctly displayed on any device, including smartphones and tablets.

How do I attach a document to a PDF?

The simplest method is to use File > New Document, and choose the option to Combine Files into a Single PDF. A file-list box will open. Drag in the files that you want to combine into a single PDF. You can add PDF files, or any combination of text, images, Word, Excel, or PowerPoint documents into the list.

How do I turn a picture into a PDF file?

Click the Select a file button above or drag and drop files into the drop zone. Select the image file you want to convert to PDF. After uploading, Acrobat automatically converts the file from image to PDF. Download your compressed PDF file or sign in to share it.

What is difference between PDF and JPG?

The main difference between JPEG and PDF is that JPEG is primarily used to compress and transfer digital images. PDF on the other hand, is used to send text, images, fonts and all other forms of information that are required to be displayed as a part of the concerned file's content.