How can I totally flatten a PDF in Mac OS on the command line?

I use Mac OS X Snow Leopard. I have a PDF with form fields, annotations, and stamps on it. I would like to freeze (or "flatten") that PDF so that the form fields can't be changed and the annotations/stamps are no longer editable. Since I actually have many of these PDFs, I want to do this automatically on the command line.

Some things I've tried/considered, with their degree of success:

• Open in Preview and Print to File. This creates a totally flat PDF without changing the file size. The only way to automate seems to be to write a kludgy UI-based AppleScript, though, which I've been trying to avoid.
• Open in Acrobat Pro and use a JavaScript function to flatten. Again, not sure how to automate this on the command line.
• Use pdftk with the flatten option. But this only flattens form fields, not stamps and other annotations.
• Use cupsfilter which can create PDF from many file formats. Like pdftk this flattened only the form fields.
• Use cups-pdf to hook into the Mac's printserver and save a PDF file instead of print. I used the macports version. The resulting file is flat but huge. I tried this on an 8MB file; the flattened PDF was 358MB! Perhaps this can be combined with a ghostscript call as in Ubuntu Tip:Howto reduce PDF file size from command line.

Any other suggestions would be appreciated.

Solution 1:

WARNING: gs and pdf2ps|ps2pdf DO NOT Flatten PDFs!

Using gs or pdf2ps followed by ps2pdf will yield a multi-layer PDF with the content under annotations present in original form. You can verify this flaw in Preview by using Select All, then Copy, then Paste into a TextEdit window (in rich text mode). You will see the text or graphics under redaction annotations for example. This is clearly very bad if you legally need that content to be gone from the output.

A Working Solution

ImageMagick can produce a configurable quality, multi-page, single-layer flattened PDF with rasters of each page using the following command:

convert -density 150 document_original.pdf document_flat.pdf

This command rasterizes document_original.pdf, making an pixel-based image of each page, at 150 DPI, and outputs the result as document_flat.pdf.

A Note on Image Quality

Due to the rasterization, it produces a non-scalable (zoom and you'll see the text or original vector images become pixellated) PDF. It will likely have a larger filesize unless the original has very complex vector content like million-point scatter plots.

By changing density, you can trade larger file size for higher resolution output.

All text will be converted to raw pixels in each page image. Text and vector diagrams suffer the most, so experiment with the DPI until you get usable output files.

Solution 2:

Try using pdf2ps and ps2pdf in succession. It's a little cumbersome but it helped me reduce my 30MB document down to 17MB. Not as much as I would have liked but still better. I got this idea from a friend who used this method to get rid of password permissions on a pdf.

pdf2ps your_pdf_file.pdf your_pdf_file.ps
ps2pdf your_pdf_file.ps your_pdf_file_from_ps.pdf

Hope that helps!

Solution 3:

EDIT 2020-07-25 This used to work but doesn't anymore. Now these commands continue to preserve the PDF layers.

So this is what I've been using lately. I think functionally it does the same thing as pdf2ps file.pdf - | ps2pdf - file_flat.pdf, but it seemed to work better for me.

gs -sDEVICE=pdfwrite -dPDFSETTINGS=/default -dNOPAUSE -dQUIET -dBATCH -sOutputFile=<newfile> <oldfile>