Cách Nén Tệp PDF Từng Bước Một
Quick Answer
Để nén PDF: mở PDF Compressor, tải lên PDF, chọn mức nén (medium thường tốt nhất) và tải xuống PDF đã nén. Tất cả xử lý xảy ra cục bộ trong trình duyệt dùng thư viện WASM —PDF không bao giờ được tải lên.
Introduction
Tệp PDF có thể lớn do hình ảnh nhúng, font và nội dung chưa nén. PDF lớn chậm khi email, tải lên và tải xuống, và có thể vượt giới hạn tệp đính kèm (thường 10-25 MB). Nén giảm kích thước tệp bằng cách nén lại hình ảnh và loại bỏ object dư thừa.
Step by Step
-
Open the PDF Compressor tool
Go to the PDF Compressor tool page. The tool processes PDFs locally using a WASM-based PDF library, so your file never leaves your browser.
-
Upload your PDF file
Click upload or drag-and-drop your PDF file onto the tool. The tool loads the file into memory using FileReader. The maximum file size depends on your browser's memory (typically 50-100 MB).
-
Select the compression level
Choose a compression level: Light (minimal quality loss, ~20-30% reduction), Medium (good balance, ~40-60% reduction), or Strong (aggressive, ~60-80% reduction, may visibly reduce image quality).
-
Compress the PDF
Click Compress. The tool processes the PDF: it recompresses embedded images at lower quality, removes redundant objects, and optimizes the structure. This may take a few seconds for large files.
-
Download the compressed PDF
Click Download to save the compressed PDF. The tool shows the original and compressed file sizes and the percentage reduction. Open the result to verify quality is acceptable.
Examples
PDF with embedded photos
Input: report.pdf (15 MB, 50 pages with photos)
Output: report-compressed.pdf (4.5 MB) — 70% reduction, photos slightly softer
Text-heavy PDF
Input: document.pdf (2 MB, 100 pages, mostly text)
Output: document-compressed.pdf (1.2 MB) — 40% reduction, no visible difference
Scanned PDF
Input: scanned.pdf (30 MB, scanned images)
Output: scanned-compressed.pdf (8 MB) — 73% reduction, text still readable
Common Problems
- PDFs with already-compressed images compress less —if images are already JPEG-compressed, further compression yields smaller reductions.
- Strong compression degrades image quality —use Medium for most cases; reserve Strong for when file size is critical and quality is secondary.
- Encrypted PDFs cannot be compressed —decrypt the PDF first (remove the password) before compressing.
- PDFs with embedded fonts may not shrink much —fonts are a significant part of some PDFs and cannot be compressed lossily.
Tips
- Use Medium compression for most cases —it provides a good balance of file size reduction and quality preservation.
- For email attachments, target under 10 MB —most email providers reject attachments over 25 MB and some over 10 MB.
- Compress scanned PDFs more aggressively —scanned pages are images, so image compression techniques work well.
- Use our PDF Compressor for private, browser-based processing —your PDF never leaves your device.