PDF export tripled in size and can't figure out why

[okapia]

I'm having a really frustrating problem with InDesign today. I'm making a 467 page document that has a lot of hyperlinks but very few images. My original InDesign file was 143mb and was exporting PDFs that were about 5mb. These were further reduced to about 3mb in Adobe Acrobat DC.

I made a copy of this InDesign file where the only changes were to be the color scheme and cover image. That's all I touched. Now, the exports with the same settings are about 15mb. Adobe Acrobat DC will only reduce them to about 10mb.

I tried using "Save As..." to "remove the gunk" (as one website put it) and carefully deleted any extrenous data in the InDesign file and got it down to 89mb, but this only shaved a few KB off my PDF exports. I tried using higher compression settings, and this shaved off a couple MB but my files look awful and it's still more than double the sizes I was previoulsy exporting. I tried removing all the images, and this only further shaved off a few more KB.

For what I'm doing, I have to get these files under 5mb each and I just can't figure out what changed that could have made the exports so large. At this point I'm going to go back to the original file, replace the colors again, and see if it exports closer to the original size this time. But I'm so confused about what could have happened. Does anyone have any ideas?

[BobLevine]

There are too many settings involved for any of to even guess, but I will give you my $0.02 on this which you can take or leave...

5MB is a tiny file and trying to get a 467-page document, even if it's just text is going to be quite a task. If Acrobat cannot do it, you're not going to be able to lower the size.

[okapia]

The original file that was exporting the 5mb files has the same number of pages and links (I didn't edit any of those). The only difference between the files is that I used Find/Change > Color to replace the color scheme and linked to a different cover image (which was actually smaller than the one in the first file). Clearly something went wrong though.

[Creamer Training]

What version of InDesign was the original PDF made in?

Can you make the InDesign and PDF available? 

[okapia]

Version 17.0 for both of them. The InDesign files are too large to upload here.

I'm going to try going back to my original file and starting over with the recolor and export after each major step to see if I can pinpoint what's causing the file size change (if it even happens again).

[Creamer Training]

You don't have to upload them. Put them in the Creative Cloud folder, wait for them to upload, and share the link (if you wish).

Go to the Optimize PDF tools and click on Advance Optimization. In the upper right corner of the dialog box, you will see an "Audit space usage..." button. Click it and see what is taking up most of the space. 

[okapia]

Update: I started over from the original file, made my changes, and am now getting PDF exports that are 4.88mb.

One of the original cover images I placed in the file I was having trouble with was a large and complex vector image with way too many points. Even though I realized it was a mistake and quickly replaced it with a smaller graphic, I suspect InDesign might still have been exporting something related to this with my file. Even using "Save as" and creating a new file didn't fix it. Otherwise, I can't think of what could have possibly caused such a file increase since I just made the same changes (except for adding a large image at some point) and the file size decreased.

[Eugene Tyson]

Save as won't do much.

You need to 

File>Export 
Choose IDML
Open the IDML in InDesign
Save the file as a new InDesign file with a new name
See if the issue persists.

[Lukas Engqvist]

If you want file size to be small and you have complex vector, consider converting that vector to image. For some images compresswing in higher resolution but heavier compression is the way to reduce the image. Also the number of fonts can affect the file size dramatically, subsetting Pro fonts will also have dramatic effect on file size.

As @Creamer Training says Audit in Acrobat is the the first step in finding how to reduce a file.in size.