Why does Acrobat sometimes increase PDF file size after editing?

Hello ​@lizetteboucher 

I hope you're doing well. We apologize for the delayed response and the trouble.

Could you please share more details about the issue/question?

• Which Acrobat version are you using (Acrobat Pro, Standard, or Reader, and version, check from Menu (Win) | Acrobat (Mac) > Help About Acrobat)?
• What OS are you on (Windows or macOS)?
• What type of PDFs are these (e.g., scanned PDFs, forms, or text-based documents)?
• What kind of edits are you typically making (text edits, comments/annotations, images, form fields)?
• Is your goal to keep file size minimal for sharing or to preserve editability for further changes?

Please note that when you make a change and use a plain Save, Acrobat does an incremental save: instead of rewriting the whole file, it appends your changes (edited text, comments, updated objects) to the end of the existing file and keeps the earlier content too.

It is fast, and it preserves a recoverable history, but each save adds to the size, so even minor edits can make a file grow noticeably over several rounds. Editing operations can also embed additional data, for example, a font subset for newly typed text, or image and annotation data for comments, which adds to the total.

How to keep sizes down without losing quality:

1. Save a fully rewritten copy instead of an incremental one. Use Menu | Acrobat > Save As (rather than Save) and overwrite the file. A Save As writes a clean, single copy without the appended change history, which often recovers most of the added size on its own.
2. Run Reduce File Size for a quick optimization. Open the PDF and go to All tools > Compress a PDF (also available as Menu/Acrobat > Save as Other > Reduced Size PDF). In the Make compatible with dropdown, keep the latest version if all your recipients use current Acrobat or Reader, since older compatibility limits compression.
3. Use the PDF Optimizer for granular control (Acrobat Pro). Go to All tools > Compress a PDF > Advanced Optimization (or Menu/Acrobat > Save as Other > Optimized PDF). It lets you tune images, fonts, transparency, and discard panels separately, so you can shrink the file while protecting quality. The Audit space usage button in that dialog is the most useful starting point, as it shows exactly what is consuming space (fonts, images, comments, and so on) so you target the real cause.

For more details, you can refer to these articles:

• Reduce PDF file size with advanced options.
• Reduce PDF file size
• Save a PDF

I hope this helps, and let us know if you need any assistance.

Regards,

Anand Sri.