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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitchesFor a preservation master where image fidelity matters, choose lossless compression. Lossy compression can make a PDF smaller by discarding image information, so it is better treated as an access or delivery choice—not a substitute for keeping a high-fidelity master. PDF/A does not, by itself, guarantee that a scan or its images were preserved losslessly.
What lossless and lossy PDF compression mean
Lossless and lossy describe how image data is encoded inside a PDF. Lossless compression preserves the encoded information exactly; lossy compression discards some information to reduce file size. The distinction matters most for scanned pages and other image-based content. It is separate from PDF/A conformance, which concerns whether a PDF meets requirements in an archival-oriented standard.
| Consideration | Lossless compression | Lossy compression |
|---|---|---|
| Image information | Retains encoded information exactly. | Discards some image information. |
| File size | Often larger for the same content and settings. | Often smaller, with quality tradeoffs. |
| Fine detail | Avoids compression-induced loss. | Depending on settings and the source, may soften or erase small features. |
| Typical role | A high-fidelity preservation master when fidelity is the priority. | A derivative for access or delivery when smaller size is worth the loss. |
There is no universal compression ratio that applies to all documents. The Library of Congress identifies lossless compression and high-resolution images as features of high-quality PDFs, but does not publish a universal file-size saving percentage for lossy versus lossless compression.
Is PDF/A lossless?
No. PDF/A is a family of ISO standards for constrained PDF files intended to support long-term preservation of page-oriented documents. It is not a guarantee that every image stream is lossless or that the source scan was captured adequately. Conformance addresses the PDF’s format requirements; preservation also depends on capture quality, quality control, and a continuing preservation plan.
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The Library of Congress describes PDF/A-1, PDF/A-2, PDF/A-3, and PDF/A-4. PDF/A-3 allows embedded files in any format, so an institution may need to decide whether those attachments are part of the preservation payload and how to preserve them. PDF/A-4 is based on PDF 2.0 (ISO 32000-2:2020). These differences do not establish one version or compression setting as right for every archive.
For scanned works, the Library of Congress says that source images are usually considered the master format when available, and that PDFs made from them may be optimized for access convenience rather than sustainability. In other words, a PDF/A made from a scan should not automatically be treated as the lossless original.
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Choose compression according to the PDF’s role
Preservation master
If retaining image detail is the priority, use a lossless approach for the master. Keep the original scanned image files as the master when they are available, along with the preservation metadata and integrity controls required by your institution. The PDF may be a useful representation of the material, but it need not replace the source images.
Access or delivery copy
A lossy PDF may be appropriate when a smaller file is important for distribution or convenient viewing and the detail loss is acceptable. Make that decision against the actual pages rather than an assumed size saving. Check small text, line art, stamps, and faint marks at realistic viewing or print size; these are the details most likely to reveal a quality tradeoff.
Rank #3
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Born-digital PDF
For a PDF that did not originate as page scans, first identify what the document contains and what must remain usable. The scan-master guidance does not automatically apply to every born-digital document. Choose a preservation format and compression treatment according to the document’s structure, accessibility needs, embedded content, and institutional policy.
A practical archival workflow
- Identify the source. Determine whether the collection contains born-digital PDFs or scanned page images.
- Keep scan masters. When source images exist, retain them as masters and manage their preservation metadata and integrity controls under institutional policy.
- Create an access PDF if needed. Choose compression according to required fidelity and access constraints; use lossless compression when the PDF itself must retain high image fidelity.
- Apply PDF/A requirements where needed. Select a conformance profile appropriate to the document and validate the resulting file with a suitable tool. Validation establishes conformance, not that the source capture was adequate.
- Document the decision. Record the role of each file—master or access copy—and the preservation requirements that drove its format and compression choices.
The Library of Congress Recommended Formats Statement favors PDF/A for textual works and electronic serials. Its current 2025–2026 statement lists both PDF/UA and PDF/A as preferred page-layout formats and describes high-quality PDFs as including searchable text, embedded fonts, lossless compression, and high-resolution images. These are format preferences and quality features, not a universal compression recipe.
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- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
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What to compare before accepting a compressed PDF
- Fidelity: Does the file retain the detail required for the preservation purpose?
- Reversibility: Was information discarded during compression? Lossy encoding cannot recover detail that was removed.
- Legibility: Are fine text, line art, stamps, and faint marks still clear at the size people will view or print them?
- File role: Is this the preservation master, or a derivative made for access and delivery?
- Conformance and content: Does the file meet the required PDF/A profile, and are embedded files or accessibility needs accounted for separately?
The Library of Congress’s PDF/A Family, PDF for Long-term Preservation explains the standard family and the distinction between scanned source images and access-oriented PDFs. Its PDF Family description covers preferred PDF characteristics. The Recommended Formats Statement 2025–2026 sets out the Library’s current format preferences.
Quick Recap
Best Value
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- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
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