Reduced PDF file size doesn't work - why?

[spinachworld]

I work a lot with .pptx files that I then convert to PDFs to email to clients.  The initial PDF file may be anywhere from 10-20mb or larger, so I always reduce the size for ease of emailing.  I use Save As Other>Reduced Size PDF and then I select compatibility with "8.0 or later", which seems to work for most of my clients.  Usually this reduces the PDF to anywhere from 1.5-3mb (depending on how large the original was), which works fine.

Here's my problem:  certain PDF files seem to be resistant to being reduced.  For example I currently have an original file that's 11.7mb and when I follow the procedure described above, the file size doesn't reduce, even when I change the compatibility settings to "10.0 or later".  It stays at 11.7mb even though it appears to be going through the process of reduction.

These files are all created exactly the same way and have no additional graphics or other elements that might add to the file size.  So why do some PDFs reduce and others not?

[try67]

There's no easy way to answer that, since we don't know what the file is composed of. You can view it by going to the Content panel in Acrobat, right-clicking the top-level item and selecting Audit Space Usage. You will see something like this:

If most of the file-size is composed out of images or fonts, that might explain why reducing the file size doesn't have much of an effect. You will need to remove (or subset) the fonts and decrease the quality of the images to achieve a smaller file-size in that case.

[spinachworld]

OK, so I just followed your instructions and discovered what the difference appears to be.  I opened two nearly identical PDFs and did the Audit Space Usage.  On the one that didn't reduce, there's a category called "Piece Information" that accounts for nearly 40% of the size.  On the one that reduced properly, the Piece Information category doesn't even exist.    Both of these PDF's were created from the identical .pptx template, within days of each other, with no changes to the images, fonts or basic substance of the text.  What would cause one to have all the additional piece information and the other not?

[try67]

It's a previous version of the file. Use the Save As command and save it under a new name and I believe it will get rid of it.

[spinachworld]

Nope, didn't work.

[kruken]

I'm having the same issue, with a 40 MB PDF consisting of 97% "Piece Information"

Was able to get rid of it using the PDF Optimizer on the Discard User Data tab and hoping it didn't break anything