How to Reduce PDF Size Without Ruining It

To reduce a PDF's size, open it in a compressor, choose a lower image quality, and check the result before you send it. Most of the weight in a PDF sits in images, so that is where compression pays off. With FlowPDF, you can do this in your browser. Your file never leaves your device, and there is no signup, subscription or watermark.

This guide shows what makes PDFs large, how to hit the limits Singapore portals set, and how to shrink a file while keeping text and signatures readable.

TL;DR

• ✓ Images and scans cause most PDF bloat. Compressing them gives the biggest savings with the least visible loss.
• ✓ Singapore portals set hard caps: ICA asks for under 2MB per document, and HDB allows up to 5MB per file.
• ✓ Use the mildest setting that gets under your limit, then zoom in on small text and signature pages.
• ✓ Compress before you sign. Changing a signed file can break the signature.
• ✓ FlowPDF compresses locally, so contracts, IDs and payslips are never uploaded.

Table of Contents

• Why your PDF is so large
• Lossy or lossless: what you trade
• Singapore limits you will actually meet
• How to reduce PDF size with FlowPDF
• Fix the file before you compress it
• Keep quality: what to check after compressing
• Compress first, sign last
• Our view: privacy comes before size
• Try it on your next file
• FAQ
• Sources

Why your PDF is so large

A PDF is a container. It holds text, fonts, images, and sometimes attachments or hidden data. Pure text pages are tiny. Size grows when the container holds heavy parts.

Scanned pages. A scan is a picture of a page. If the scanner stores that picture with lossless compression, a single page can become very large. A practitioner case study explains that converting such images to JPEG-style compression can cut size by more than 85% with no visible loss on screen.

Embedded fonts. Some files embed an entire font instead of only the characters used. The same case study notes that a full CJK font can add 10MB to 20MB, and that keeping only the glyphs actually used can shrink that part by around 95%. This matters for documents with Chinese, Malay or Tamil text mixed in.

High-resolution photos. A photo taken on a phone is far sharper than a screen needs. Dropping it to screen resolution saves a lot of space.

Duplicate content. Files merged from many sources can carry the same image or font several times.

Knowing which of these applies to your file helps you pick the right fix. A scan needs image compression. A text-heavy report with huge fonts needs a different approach. A 300-page photo book needs both.

Lossy or lossless: what you trade

There are two ways to make a PDF smaller.

The same case study describes lossy compression as permanent pixel removal that suits screen viewing, and lossless methods as keeping full quality at the cost of smaller reductions.

In practice, "compress without losing quality" means one of two things. Either you choose a light lossy setting where the loss is invisible at normal zoom, or you accept a smaller saving. No tool can promise a 90% cut with zero change to a photo-heavy file. Keep the original and work on a copy.

Singapore limits you will actually meet

In Singapore, the reason most people search for this is a rejected upload. These are the limits we found on official pages:

Limits change, and each form or e-service can set its own. Read the notes on the upload page you are using before you start. The MOM FAQ is dated 2019, so treat the upload page itself as the final word.

Two details trip people up:

• Password protection. ICA says the file should not be password protected, and HDB says files must not be encrypted. If your bank statement is locked, remove the password first. Our guide on removing PDF restrictions without uploading covers it.
• Per document, not per batch. A 2MB cap applies to each file. If you have one 9MB file with ten pages, you can also split it into parts and compress each. See Split PDF.

How to reduce PDF size with FlowPDF

FlowPDF runs in your browser. Processing happens on your device, so a passport scan or an employment contract is not sent to any server.

1. Open FlowPDF Compress PDF.
2. Add your PDF from your computer or phone.
3. Choose a compression level. Start with the lightest one.
4. Run the compression and check the new file size.
5. Open the result and zoom in on small print, stamps and signatures.
6. If it is still over your limit, repeat from the original with a stronger setting. If it looks too soft, go one level lighter.
7. Save the file under a new name, so the original stays safe.

Two things we recommend: always start from the original file, not from an already-compressed copy, and avoid compressing the same file again and again. Each lossy pass removes more detail.

If you have a specific target, these guides go deeper:

• Reduce a PDF to 1MB for forms with a tight cap.
• Shrink a PDF to 200KB for strict upload fields.
• Compress on Android and compress on Mac for device-specific steps.

Fix the file before you compress it

Sometimes the best way to reduce PDF size is to make the file smaller at the source.

Remove pages you do not need. A cover sheet or blank back page costs space. Use Remove Pages or Extract Pages to keep only what a form asks for.

Crop empty margins. Scans often include a dark border. Crop PDF trims the visible area.

Scan smarter. MOM's guidance is that scanners should be set to at least 150 dpi, and the same FAQ prefers colour but allows other modes. Greyscale is often enough for text-only documents and can roughly halve the size of a scan compared with colour. If you want to understand how resolution relates to quality, this Italian-language guide to PPI and DPI has a useful table, even though it is written for print. For screen and upload use, 150 to 300 dpi is usually enough to stay readable.

Merge last, not first. If you are combining papers into one file, compress the large pieces first or compress the final merged file once. Merge PDF works locally too.

Keep quality: what to check after compressing

A smaller file is only useful if the recipient can read it. Run this check each time:

• Zoom to 150% on the smallest text, such as footnotes, tables and fine print.
• Look at signatures and stamps. Thin pen strokes can turn muddy or broken when a file is over-compressed. The case study mentioned earlier advises checking signature pages specifically.
• Check photos of faces or IDs. If an authority asks for clear images, a blurry ID photo can lead to a rejected application.
• Scroll the whole file. Make sure no page is missing or rotated. Organize PDF fixes order and rotation.

If text looks fuzzy, do not push the setting further. Go back to the original and use a lighter level, or remove pages and crop instead.

Compress first, sign last

If your document carries a certificate-based digital signature, compressing or editing it afterwards changes the file's bytes, so the signature can no longer be verified. The safe order is simple: edit, compress, check, then sign.

For a visual signature drawn or typed onto the page, the same order still helps. You avoid degrading the signature image with a later compression pass. FlowPDF's Sign PDF works locally. Note that it is not meant for certificate-backed digital signatures, so if a counterparty requires one, use a provider they specify. Our guide to signing PDFs locally walks through the steps.

Our view: privacy comes before size

We built FlowPDF around one idea: you should not have to hand a document to a stranger's server just to make it smaller.

Think about what people compress for upload. A scanned NRIC, a payslip, a tenancy agreement, a signed contract. These are the most sensitive files you own. Many popular online compressors work by uploading your file, processing it on their servers, and sending it back. That is convenient, but it adds a step where your document sits somewhere you do not control.

With FlowPDF, the work happens in your browser tab. There is no upload step, no account, no watermark and no price. We do not earn money from subscriptions or ads, so we have no reason to keep your file or your attention.

We also think honest limits matter. Compression is a trade. We will not promise a tenfold reduction with no change at all, because physics and file formats do not work that way. Our advice is to use the lightest setting that clears your limit, check the file, and keep your original.

And if you need advanced paid features or certificate-backed signatures, FlowPDF is not the tool for that. For everyday compressing, merging, splitting and signing, it covers what most people need.

— Ronald Ang

Try it on your next file

Open FlowPDF Compress PDF, add your file and see the new size in seconds. If you need more than compression, the full toolkit includes edit, merge, split, redact, protect and more. Everything is free, and every file stays on your device. To lock a file after compressing, see protecting PDFs without Adobe.

FAQ

How do I reduce PDF size without losing quality?

Use the lightest compression level that gets you under your limit, and start from the original. Light lossy compression on images is usually invisible at normal zoom. Zoom into small text and signatures afterward to confirm. If you need exact fidelity, expect smaller savings.

How can I get a PDF under 2MB for ICA or MOM?

Compress it, then check the size in your file manager. If it is still above 2MB, try a stronger setting, remove unneeded pages, or crop margins. For new scans, 150 dpi is the minimum MOM recommends. Also make sure the file has no password, as ICA requires.

Is it safe to compress a PDF online?

It depends on how the tool works. Many online compressors upload your file to a server. FlowPDF processes your PDF locally in your browser, so the document is not uploaded. For IDs, contracts and financial documents, a local tool is the more careful choice.

Why is my PDF still big after compressing?

The file may already be well compressed, or the weight may be in fonts or many high-resolution images. Try removing pages, cropping, or re-scanning in greyscale at a lower resolution. A PDF/A file can also stay larger, because the standard requires full font embedding and favors archival integrity over minimum size.

Sources

• ICA Technical Help
• HDB on Ask.gov.sg: what type of documents can be uploaded
• MOM e-submission FAQ
• PDF Compression in 5 Steps: 80MB to 8MB Case Study, DEV Community
• PDF/A (ISO 19005) overview, DEV Community

Recommended

• How to Reduce a PDF to 1MB Fast, Without Losing Quality
• Shrink PDFs to 200KB Locally, Aim for 180KB and Keep Quality
• Shrink PDFs on Android to 1 MB or Less, No Upload, Keep Readability
• Compress PDFs Offline in Under a Minute, No Upload