A PDF that's 15 MB when it should be 1 MB is a common problem. Email clients reject it, upload forms refuse it, and Google Drive storage warnings kick in. Knowing how to reduce PDF file size is one of those skills that saves you from repeated frustration.
This guide covers five methods, from quickest to most thorough, so you can pick the right approach for each situation.
Method 1 — Online PDF Compression (Fastest)
For many PDFs, an online compression tool is the quickest first step. The Compress PDF tool on this site runs in your browser — no upload to a server, no account, no cost.
When to use: Any PDF where the content is finished and you just need a smaller file, especially one that was saved by a tool that doesn't compress its internal structure.
How it works: The tool uses pdf-lib to re-save the PDF with its internal structure (object and cross-reference data) packed using deflate compression. It does not re-encode images or text, so quality is identical to the original. You choose a compression level:
- Maximum — packs the structure for the smallest file
- Standard — a good balance of size and compatibility (the default)
- Minimal — keeps the original structure for the best compatibility with older PDF readers
Typical savings are around 5–40% for PDFs that weren't already optimised, and little or nothing for PDFs that already were. Files are limited to 50 MB.
Steps:
- Go to Compress PDF
- Upload your PDF
- Select your compression level (Standard works for most cases)
- Click Compress and download
Because this method doesn't touch the images, it can't fix a PDF that is large mainly because of high-resolution photos or scans. For that, use the methods below.
Method 2 — Remove Unnecessary Pages
If your PDF contains pages you don't actually need — blank pages, duplicate copies, old versions of a page, appendices the recipient doesn't need — removing them is the most permanent and lossless way to reduce file size.
Use the Extract PDF Pages tool to keep only the pages you need:
- Upload your PDF (up to 50 MB)
- Select the pages you want to keep by clicking their thumbnails
- Download them as a new PDF
(The Split PDF tool can also cut a PDF into parts by page range, such as "1-10, 15-20", but it creates a separate PDF for each range.)
This approach has zero quality impact — you're simply discarding pages, not recompressing anything.
Method 3 — Compress Images Before Creating the PDF
If you're generating the PDF yourself from images, Word documents, or design software, reducing the image resolution before creating the PDF produces the smallest possible result.
For photos and scans: 150 DPI is sufficient for screen viewing. 300 DPI is needed for printing. If the PDF will only be read on screen, resizing scanned images to 150 DPI before creating the PDF can cut image file sizes by 75%.
If you're working with images directly, use the Compress Image tool to reduce image sizes before inserting them into your document.
Method 4 — Flatten Annotations and Form Fields
PDFs that contain interactive form fields, annotations, and comments store these separately from the page content. In some cases, these interactive layers add significant overhead.
After users fill in a form, "flattening" the PDF merges the form data into the static page content, which prevents the fields from being edited and may slightly reduce file size.
The Flatten PDF tool on this site converts interactive form fields (text boxes, checkboxes, dropdowns) into static page content, which stops them from being edited. Treat it mainly as a way to lock in filled-in forms; it only affects form fields, not comments or other annotations, and any size reduction is usually small. It runs in your browser.
Method 5 — Re-Export with Smaller Fonts and Metadata
PDFs can contain extensive metadata: author name, creation software, revision history, and more. Some PDFs also embed large fonts that could be subsetted (only the characters actually used included) rather than fully embedded.
This is best fixed at the source: when you export from Word, InDesign, or LibreOffice, use the "minimum size" or "web" export preset, which subsets fonts and downsamples images. The Compress PDF tool does not strip metadata or subset fonts, so it can't help with this part.
What Is Causing My PDF to Be Large?
Before choosing a method, it helps to understand what's making the file big:
| Likely cause | Best fix | |-------------|----------| | High-res scanned or photo images | Re-export the source with lower-resolution images; Compress Image first | | PDF saved without structure compression | Compress PDF (Maximum or Standard) | | Many pages, some unneeded | Extract PDF Pages to keep only what you need | | Interactive form fields | Flatten PDF (small effect) | | Lots of embedded fonts | Re-export from the source with font subsetting |
If your PDF barely shrinks after compression, it's likely already well-compressed, or the file size is coming primarily from images or fonts, which this tool leaves untouched.
Target File Sizes by Use Case
| Use case | Target size | Method | |----------|------------|--------| | Email attachment | Under 10 MB | Compress PDF, plus extracting only the pages you need | | Email attachment (tight limit) | Under 5 MB | Extract needed pages, or re-export with lower-resolution images | | Web page download | Under 2 MB | Re-export from the source with a "web" preset | | Google Drive / cloud share | Under 25 MB | Compress PDF (Standard) | | Print file | No limit needed | Skip compression, or use Minimal | | Long-term archive | Under 10 MB | Compress PDF (Standard) |
When Not to Compress
Avoid aggressive image downsampling when you re-export if:
- The PDF contains technical diagrams where fine detail matters
- The PDF will be printed professionally (heavy image compression introduces JPEG artefacts)
- The file is a legal original that needs to remain unaltered
The Compress PDF tool itself doesn't change image quality, so it is safe for these cases. If it doesn't shrink the file enough, focus on removing unnecessary pages instead.
Related Tools
- Compress PDF — repack a PDF's structure in your browser in one step
- Extract PDF Pages — keep only the pages you need to cut file size permanently
- Split PDF — cut a large PDF into smaller parts by page range
- Merge PDF — recombine split parts when needed
- Compress Image — reduce image sizes before inserting them into documents
Try it free — no signup needed
Most tools run in your browser, so your files stay on your device. A few upload the file to our server and delete it afterwards.