Skip to main content
Tommy J.
Tommy J.
Known Participant
March 14, 2019
Répondu

Size of single combined PDF file is smaller than the total size of the original files

I have several PDF files that I'd like to combine into one single PDF file, so I used the "Combine Files" option in Acrobat DC. However, after creating that single PDF file I noticed that its size is 245 MB while the total size of the combined files is 321 MB!

In the "Options" window I selected the "Larger File Size" option and left all other options in the list unchecked. So provided that there wasn't any compression or downsampling during the combination process, shouldn't the file size of the single PDF file be the same as the total size of the combined files? Has anybody else noticed that again?

Thank you

Ce sujet a été fermé aux réponses.
Meilleure réponse par gary_sc

Hello Gary and thanks a lot for taking the time to reply.

I have one big question for you in regards to how the scans were done: What was the resolution of the original scans and what format were the documents saved as. This can have considerable dynamics as to how things will appear in both original and subsequent digital copies.

It's been my experience that many people default to saving scans into JPG format. If you did that, and I do not know if you did or not, than that is a bad place to start. Plus, when saving a PDF, one can set the amount of compression during the saving process to reduce the size of the document (from little to a lot of compression).

Yes, I did the book scanning myself. I was scanning each page in 300 DPI and then saved each one separately through Photoshop CS6 in PDF format. Here are the compression settings that I used:

Unfortunately Adobe dumbed down their interface here so you do not really know the dynamics of what's taking place here but if you mouse-over the three options you can at least see "sort of" what's taking place here. In the Combine Files window, if you click on the gear icon you can see the three options. You can see which one you need to correct if you feel you need it.

But keep in mind, if you do not SEE any visible difference between your original scanned documents and the combined document, there's no real need to do this.

Right on, I noticed that and performed again the combination process after selecting the third option called "Larger File Size". However, even then the size of the single file was only about 15 MB larger than before when the second option was selected. It still didn't even come close to the total size of the separate PDF files.


Hi Tommy,

Thank you for mentioning you created the PDFs from Photoshop, that may explain everything. Creating PDFs from Photoshop (for reasons that I do not know or understand) tend to be a bit bloated. Thus, it's probable that Acrobat removed some of this bloating during the collection process.

FWIW, when I am scanning documents that I wish to eventually turn into PDFs, I scan them as TIF documents and then let Acrobat convert those into PDFs. The storage size of TIF scanned documents is huge but once converted into PDFs via Acrobat are very small.

But the big important question is: is the quality of the PDFs any different from the individual PDFs than the full collection? If not than Try67's comment is the correct one in that there was simply some source components that were efficiently used.

It should not in any way affect the quality of the final PDF. Unless the final document is not as good as the proto-PDFs, you should be good to go.

1 commentaire

try67
Community Expert
try67Community Expert
Community Expert
March 14, 2019

Not necessarily, if the files shared some resources (like a font) Acrobat will only use a single copy of it in the merged file, so the total file-size can certainly be smaller than the sum of the source files. Also, it's possible the files are optimized after being merged and some unused resources were removed as a result.

Tommy J.
Tommy J.Auteur
Known Participant
March 14, 2019

Thanks a lot for your reply try6!

In my case the files that I tried to merge are bitmap scans of a book, so as far as I know there can't really be any shared resources between them as they are simple bitmap files. Therefore I'm afraid that Acrobat downsamples or compresses by default the files during the merging process, which is something that I don't want to happen.

If it helps, I tried to use a different application to combine the files and the single file that was generated was 320 MB, which matches almost exactly the total size of the original separate files (321 MB).

gary_sc
Community Expert
gary_scCommunity ExpertRéponse
Community Expert
March 14, 2019

Hello Gary and thanks a lot for taking the time to reply.

I have one big question for you in regards to how the scans were done: What was the resolution of the original scans and what format were the documents saved as. This can have considerable dynamics as to how things will appear in both original and subsequent digital copies.

It's been my experience that many people default to saving scans into JPG format. If you did that, and I do not know if you did or not, than that is a bad place to start. Plus, when saving a PDF, one can set the amount of compression during the saving process to reduce the size of the document (from little to a lot of compression).

Yes, I did the book scanning myself. I was scanning each page in 300 DPI and then saved each one separately through Photoshop CS6 in PDF format. Here are the compression settings that I used:

Unfortunately Adobe dumbed down their interface here so you do not really know the dynamics of what's taking place here but if you mouse-over the three options you can at least see "sort of" what's taking place here. In the Combine Files window, if you click on the gear icon you can see the three options. You can see which one you need to correct if you feel you need it.

But keep in mind, if you do not SEE any visible difference between your original scanned documents and the combined document, there's no real need to do this.

Right on, I noticed that and performed again the combination process after selecting the third option called "Larger File Size". However, even then the size of the single file was only about 15 MB larger than before when the second option was selected. It still didn't even come close to the total size of the separate PDF files.


Hi Tommy,

Thank you for mentioning you created the PDFs from Photoshop, that may explain everything. Creating PDFs from Photoshop (for reasons that I do not know or understand) tend to be a bit bloated. Thus, it's probable that Acrobat removed some of this bloating during the collection process.

FWIW, when I am scanning documents that I wish to eventually turn into PDFs, I scan them as TIF documents and then let Acrobat convert those into PDFs. The storage size of TIF scanned documents is huge but once converted into PDFs via Acrobat are very small.

But the big important question is: is the quality of the PDFs any different from the individual PDFs than the full collection? If not than Try67's comment is the correct one in that there was simply some source components that were efficiently used.

It should not in any way affect the quality of the final PDF. Unless the final document is not as good as the proto-PDFs, you should be good to go.

Conditions d'utilisationAccessibility statement
Using the community Terms of use Privacy Cookie preferences Do not sell or share my personal information ad choicesAdChoices