A PDF that shrinks only slightly does not necessarily indicate a failed operation. Choose a method based on the file's contents and what the recipient needs to do with it, especially when searchable or selectable text matters.
What the two modes do
Compress PDF currently offers these approaches:
| Mode | How it works | Suggested starting point |
|---|---|---|
| Normal, preserving quality | Compresses structures and data streams without turning every page into a picture | Documents whose text and structure need to remain |
| Strong, intended for scans | Renders each page to JPG and assembles a new PDF | A reading copy where losing text selection is acceptable |
Strong mode removes the original selectable text. It should not replace a form that still needs to be filled. A similar appearance does not imply that all document functionality survives.
Why the result may remain large
Adobe's PDF Optimizer guidance distinguishes images, fonts and objects. It explains that downsampling reduces image data and JPEG quality changes can discard data permanently. Different PDFs therefore need different expectations.
Our normal mode does not turn whole pages into lower-resolution pictures. Image-heavy scans may shrink only a little. A small text document is not automatically a good candidate for rasterisation simply because a smaller file is desired.
Our suggested workflow
- Keep the original and try normal mode first.
- Compare the downloaded file's size with the destination's limit.
- If it is still too large and only a reading copy is needed, try strong mode from the original.
- Inspect every page, particularly Thai marks, small numbers, stamps and visible signatures.
- Choose a copy meeting both readability and size requirements, not merely the smallest result.
This checklist is our recommendation. Any explicit quality or document requirements from the receiving organisation take precedence.
When compression is not enough
If the recipient allows only relevant pages, use split PDF and verify that all required pages remain. If the whole document is required, do not remove pages simply to meet a size limit. Re-export from the source document or ask about another submission route.
There is no guarantee that every document can be reduced below 1 MB or another fixed target. Recompressing an unclear copy cannot restore lost detail. To extract text from scanned images, see Thai OCR from PDF, which describes a separate step.
