Flattening a PDF file

My mother is a graphic and book designer. As part of her work, she sends drafts and previews to the customers for them to review. While she has a loyal and trustworthy clientele, some one-time customers may try to take advantage to get free or “cheap” designs. They initially agree to a service that include design and printing, but once they get the design, they disappear without notice. Sometimes they only paid a small advance, sometimes they paid nothing before disappearing. One way to mitigate this is not to provide samples in vector formats. If they receive a JPEG image, for example, they will not be able to edit it freely or print it with a different company.

It is easy to export single-page designs as images in vector graphics software like CorelDRAW and Adobe Illustrator. However, in the case of books with tens or even hundreds of pages, it usually requires the user to export page by page. If done successfully, it results in a folder with many images, which is not easy to view. Combining all the images into a single PDF file is possible, but the process of exporting page by page is still tedious.

I had the idea of automating the process for my mother. For her, it is easier to generate a PDF file with the whole book, so I used this as input. ImageMagick is a powerful tool converting and processing images. Last year I discovered that it also supports PDF files with the help of Ghostscript. In the ImageMagick forum, I found that its magick command allows a PDF file as input to return a flattened PDF file. A “flat” PDF is a PDF where all interactive, editable, and vector elements were removed, typically by merging them into a single static image of the page.

The minimal example given in the post is the following.

magick -density 1200 in.pdf out.pdf

Option -density 1200 indicates a pixel density of 1200 pixels per inch (ppi).

I extended the command call to perform JPEG compression with a given quality (integer between 1 and 100). I also convert the color space to RGB. The input PDF file is likely to be CMYK since it is the standard for printing. However, CMYK results in larger files than RGB and is not intended for viewing on screens. Option -units PixelsPerInch is used to correctly set the density in the image metadata (I learned this some time ago). Finally, -verbose shows the internal command calls—I like seeing the messages to track the process. The user can tweak the values of density and quality to achieve the desired file size and resolution. My command looks like follows.

magick -density 150 -units PixelsPerInch
	   -compress jpeg -quality 50
	   -colorspace RGB
	   -verbose
	   in.pdf
	   out.pdf

This command call generated the PDF book preview that my mother was expecting. It was smaller than the original PDF file (52 MB compared to 101 MB), the content was not selectable or editable, and resolution was sufficient for review.

Since my mother is not proficient at using computers, a command line interface was inconvenient, so I programmed a simple graphical interface. I asked Microsoft Copilot for a way to program a simple graphical interface without installing compilers or interpreters on my mother’s computer, and it told me about Windows HTML Applications (HTAs). Their source code consists of HTML and JScript (a language of the JavaScript family). This was perfect for me since I’ve been learning web design with my website. I tried to make the interface as easy as possible. I only added three fields: input file, pixel density, and quality. My mother understands these parameters and approved their defaults (150 ppi and 50). Still, I included a brief description of each parameter. The output file is saved in the same folder as the input file. File name is the same but with the word “CONVERTED” appended.

The graphical interface is shown below. The green button starts the PDF flattening. It shows a command line window with the verbose output that closes when finished.