Hi folks,

In some previous articles, we’ve mentioned that Progressive JPEG, GIF, and PNG graphic formats provide a feature allowing partial but intelligible display of the image during its download even before the download is actually finished.
Once the download is complete, the file gets fully available.

Living in a fast-paced world

The motif for providing such a feature is users’ impatience.
Bigger sized files taking time to download fully might make users get frustrated because of the delay so an initial prompt displaying, even incomplete, helps a lot to overcome the inconvenience.

For this same reason, a special variant of PDF named “linearized PDF” (or “web-optimized PDF” or “fast web view enabled PDF“) was made available starting with PDF 1.2, and today we are going to tell you few words about it.

How does a linearized PDF work?

Basically, a web-optimized PDF is a PDF allowing a “streaming“-like behavior.
More precisely, this translates into a fast display of the first page in the browser while the rest of the multipage PDF file is still being downloaded.
It also translates into displaying any other page requested by the user as quickly as possible and in such a manner to allow the user to interact with it (such as clicking on a link) even before it has been entirely received and displayed.

All these are made possible through a unique organization of the PDF file.
Regular PDFs contain all file information at the end of the file, and therefore a regular PDF becomes usable only after complete download.
Linearized PDFs contain this information at the beginning of the file in addition to a special, linear structure (hence the name “linearized”) of the “fast web view”-enabled file.

All our products support PDF linearization.
With GdPicture.NET SDK, developers can provide a “Save as linearized PDF” option to users of their applications just like PaperScan and PDF Reducer do for their users.

Tips and best practices

So let us give you some hints about using linearized PDFs.

First, remember that PDF linearization feature was created for large PDF files meant to be displayed in browsers (i.e., PDF files taking longer to load in the browser because they contain lots of texts and graphics).
Therefore linearizing a single-page PDF or a small-sized, text-based multipage PDF (which loads very fast anyway) doesn’t make much sense.
Linearizing PDF files meant for non-browser use (like use from desktop, share via email, etc.) doesn’t make much sense, either.

And one last but not least remark: altering a linearized PDF (for example by modifying a form field then saving) brakes the linearization.
In such a case, the file has to be re-linearized.

I hope this short overview shed some light on fast web view PDF.
You will find more information about PDF linearization in Annex F in ISO 32000-1 and the specification here.

See you next week, folks!


03/12/20 note:

The latest blog article from The Signal, the Library of Congress blog, mentions that the Recommended Formats Statement (RFS) includes web-optimized PDF as an acceptable format. In this article, you will find more information about the major role of PDF for long-term archiving.