PDF Compressor - Reduce PDF File Size Online Free

Compress PDF files online free — no signup required. Choose low, medium, or high compression. Your PDF is processed securely and returned instantly. Download your smaller PDF in seconds.

Click to upload or drag & drop your PDF

PDF only · Max 20 MB

Compression Level

ℹ️

Server-Side Compression

Your PDF is sent to our secure server, compressed using advanced algorithms, and returned to you immediately. Our server does not save your file.

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What is PDF Compression?

PDF compression is the process of reducing a PDF file's size. A PDF file contains many components: visible content (text, images, vector graphics), embedded fonts, document metadata (author, title, keywords), and internal bookkeeping structures. Images are usually the largest part, so our server mainly shrinks the images and repacks the file's internal structure. Text stays sharp at every level, while images may lose some detail at the higher compression levels.

File size matters because email providers like Gmail limit attachments to 25 MB, WhatsApp limits PDFs to 100 MB, many website upload forms reject large files, and smaller files transfer faster over slow connections.

How to Compress PDF Online

Click the upload area or drag and drop your PDF file (max 20 MB)
Choose a compression level — Low, Medium, or High
Click the Compress PDF button
View the before/after size comparison and savings percentage
Click Download Compressed PDF to save the result

When to Compress PDF Files

Email Attachments

Most email providers limit attachments to 25 MB. Gmail, Outlook, and Yahoo Mail all enforce this limit. Compressing PDFs ensures they can be sent without rejection errors or the need to use third-party file sharing services.

WhatsApp and Messaging

WhatsApp allows PDF files up to 100 MB. Compressed PDFs load faster on mobile networks and consume less data for the recipient — important when sharing with users on limited mobile data plans.

Website Uploads

Many websites — government portals, job application forms, school admission systems — impose strict file size limits, often between 1 MB and 5 MB. Compressing PDFs before uploading avoids rejection errors.

Cloud Storage

Smaller PDF files use less quota on Google Drive, Dropbox, and OneDrive. If you store many PDF documents in the cloud, compressing them can meaningfully reduce your storage usage.

What Affects PDF File Size?

Embedded images — the single largest contributor to PDF file size
Embedded fonts — full font files are often included even for a few characters used
Metadata and document properties — title, author, keywords, producer info
Embedded videos or audio — multimedia PDFs can be very large
Number of pages — more pages generally means a larger file
Color vs grayscale content — color images are significantly larger than grayscale

Frequently Asked Questions

How does PDF compression work?

Your PDF is uploaded over a secure connection to our server, which tries two compressors and keeps the smaller result: Ghostscript, which downsamples and recompresses images, and qpdf, which repacks the file's internal structure. If neither makes the file smaller, you get your original back unchanged. Your file is not kept afterwards.

Will compression affect PDF quality?

Text stays sharp at every level, because only the images in your PDF lose detail. Low keeps images closest to the original, while High lowers their resolution and quality the most, which can be visible in photos and scans. If compression would not make the file smaller, you get your original back unchanged.

What is the maximum PDF file size?

Calcon's PDF Compressor supports files up to 20 MB. Most standard documents, reports, presentations, and forms are well within this limit.

Is my PDF uploaded to a server?

Your PDF is processed securely on Calcon's server and returned to you immediately. Our server does not save your file.

Why is my PDF not compressing much?

PDFs that are already optimized will show little reduction, and if our server cannot make the file any smaller, it returns your original unchanged. Scanned PDFs are mostly images, so the High setting, which lowers image resolution the most, usually shrinks them the furthest.

Can I compress password-protected PDFs?

The tool attempts to open encrypted PDFs. PDFs with user-level passwords that restrict opening may not compress. Remove the password first with Calcon's PDF Password Remover, then compress.

Does this work on mobile?

Yes. Calcon's PDF Compressor works on any modern smartphone or tablet browser — iOS Safari, Chrome for Android, and others. No app needed.

What is the difference between low and high compression?

All three levels run the same two compressors and keep the smallest result. The level only changes how hard Ghostscript works on images: Low reduces images above 150 DPI to 150 DPI with light JPEG compression, Medium uses 100 DPI with moderate compression, and High uses 72 DPI with the strongest compression for the smallest file.

Can I compress multiple PDFs at once?

Currently the tool compresses one PDF at a time. Batch compression is planned for a future update.

Is PDF compressor free on Calcon?

Yes, completely free. No signup, no account, no payment. Compress as many PDFs as you need at no cost.

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