Why is the file size of a merged pdf smaller than the sum of the originals (without compression)?

Forum|Forum|5 years ago
September 14, 2020
3 replies
2374 views

Hey,

I have a problem. I rendered several pdf pages out of Photoshop and want to merge them in one single pdf without compression for the printing service. I did this with the Adobe Acrobat Pro DC and the best quality settings. In my understanding this is without any new compression. After the merging process the file size of the single outcome pdf is much smaller than expected. In sum of all pages I expect about 4 gb of file size. But it is only 500 mb large. In my understanding this is not uncompressed. What did I wrong?

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try67

Community Expert

Are your files only images, or do they also contain text? If they have text then the fonts used for it might explain this.
Imagine you merge 10 files and each file has a font embedded in it that's 10MB. The merged file doesn't need to have 10 copies of this font, only one, so just there you've saved 90MB off the total size of the merged file compared to the originals, without losing any data or compressing anything...

H

Holy MountainAuthor

Participating Frequently

Hey,

thank you for your awnser! This seems logic for me. But and this the big problem. it depends not on the text (see the screenshots of the space usage of just two files). So the pictures make about 99% of the file size...

ls_rbls

Community Expert

What is the original image file type and what method did you used to merged these files together into a single PDF?

H

Holy MountainAuthor

Participating Frequently

You mean in Photoshop? I used jpegs, texts ect. Than I exported all this uncompressed as an pdf. Than I go to Acrobat Pro DC, tools, merge pdfs, options: best quality, and than merge all 13 pdfs together.