将高分辨率PDF转换为低分辨率PDF文件C＃

Question

I´m looking for a way to convert a High Resolution PDF file to a Low Resolution PDF file from an ASP.NET applicaitn (C#). Users will import High Resolution PDF's and the solution should then have the possibility to provide both High Resolution PDF and Low Resolution PDF. I´m looking for a API to do that. I have found a lot of PDF apis but none of them seems to do what I´m looking for.

Answer 1

ABCpdf .NET will do this for you. There are a variety of functions for resizing, resampling or recompressing the images within a PDF document. However given your requirements you probably just want to use the document reduce size operation.

To do this you just need code of the following form:

Doc doc = new Doc();
doc.Read(Server.MapPath("../mypics/sample.pdf"));
using (ReduceSizeOperation op = new ReduceSizeOperation(doc)) {
op.UnembedSimpleFonts = false; // though of course making these true...
op.UnembedComplexFonts = false; // ... would further reduce file size.
op.MonochromeImageDpi = 72;
op.GrayImageDpi = 72;
op.ColorImageDpi = 144;
op.Compact(true);
}
doc.Save(Server.MapPath("ReduceSizeOperation.pdf"));

I work on the ABCpdf .NET software component so my replies may feature concepts based around ABCpdf. It's just what I know. :-)

Answer 2

Probably you can just resize images in high resolution version PDF and this will give you much smaller files.

You can resize and/or recompress images using Docotic.Pdf library . For more details please take a look at my answer to a similar question .

Disclaimer: I am one of the developers of Docotic.Pdf library.

Answer 3

There are a number of possible approaches to this problem, one of which would simply be to export from InDesign twice (which would allow you to make the two required versions of PDF). If that is not feasible (which it might not be as exporting from InDesign can take a bit of time) there are definitely libraries on the market that can perform what you want to do. Here to you have a number of approaches:

1) While this will get me shot by most Adobe employees, you could re-distill your PDF file into a smaller file. I would not advocate to do this, I'm mentioning it to be complete. Risks involved would be introducing quality loss, artefacts and so on (mostly because PostScript doesn't support a number of features PDF does support and by redistilling you'd loose those features).

2) Use an application or library that was made for this task. callas pdfToolbox for example (warning, I'm affiliated with this company!) is capable of taking a PDF file and running corrections on it. Amongst those corrections are image downsampling, conversion to RGB, image re-compression (for example with JPEG-2000), throwing away unnecessary data in the PDF and much more. Given that the application has a command-line interface, it can easily be integrated into ac# process. Other applications with similar functionality would be from companies such as Enfocus, Apago and others.

3) Use a low-level PDF library (such as the Adobe PDF library that can be licensed from Adobe through DataLogics) and implement the necessary changes yourself. More work, but potentially more flexible.

Whatever approach you choose, know that you are starting from a high-quality PDF file and that your process should try to retain as much of that quality as possible (dependant on which application you have for the low resolution PDF file of course). Make sure you don't get into trouble by loosing proper overprint, transparency etc...