Why do some PDF's come out at massive filesize?

[OHCreative]

I had to do a postcard design for a client - i.e. A6.  Did the design, output the PDFs for front and back seperately, and they came out at 40mb and 50mb.

Sent to client who said "Can they be smaller?  Last ones you did were only around 1mb."

I checked, client was correct.  I thought maybe there was some metadata in there or something (there wasn't), or perhaps the resolution was different, but in fact the smaller PDF's from the previous job were actually 600dpi, wheras the new ones were at 300dpi. Other than that they were the same - CMYK, a couple of placed JPEGS and a few lines of text turned to shapes.

After a couple of hours trying to work out why the filesizes were so large I gave up.  However, as a test I moved the layers from the master PSD into a new PSD, at the same size, same DPI, and CMYK... and output the PDF's again.  This time they came out at around 4mb.

So, what's happening here?  How is it possible to export the exact same layers as a PDF from two different 'identical' PSDs, that have such vastly different PDF file sizes?

[jane-e · Accepted solution]

@OHCreative 

One thing you might try is to open each PDF in Adobe Acrobat Pro, then choose Advanced Optimization from the Optimize PDF tool.

In the PDF Optimizer dialog, first click "Audit space usage" in the upper right and compare the two PDFs. Then click on each tab on the left and, again, compare the two PDFs.

You can also use this dialog to reduce the size of a PDF. Do it on a copy.

Jane

[OHCreative]

Jane, thank you - this was enlightening 🙂  So the documents, when compared, showed that the larger of the files had 88.5% in "Document Overhead" - a total of 36mb. The smaller file had around 1.5% Overhead.

So, what is Document Overhead??

[jane-e]

It's a good question, @OHCreative , and I hope other volunteers will chime in if they know something.

I just did a little searching and the best article I came up with was from the illustrious @davidblatner  of Creative Pro fame. He wrote this in 2011 with Acrobat 9 and InDesign, but it still applies. He was able to reduce the size two ways: in Acrobat and by creating the file a different way.

https://creativepro.com/document-overhead-in-indesigns-pdf-can-be-huuuuuuge/

I wonder: did you start with PDFs in Photoshop and then make a new PDF? If not, what did you start with?

Jane

[OHCreative]

Both files were started from, literally, a blank page using Photoshop's New Document panel, so it's really odd that this Document Overhead appeared.  I wonder if it could have been pulled in, if you like, from using Place Linked / Embedded.  However, I rasterised everything before output so you'd think that any meta / Overhead info would be stripped out... 

I'd be interested to see what other experts suggest. 

Meantime though, thank you sincerely for taking the time to help!