PDF to PDF Conversion Tips: Reduce File Size, Change Version, and Keep Fonts

Guide — PDF to PDF: Preserve Formatting When Converting and Re-exportingPreserving formatting when you convert, edit, or re-export a PDF can feel like walking a tightrope: one wrong setting and fonts shift, images blur, or interactive elements break. This guide explains why formatting changes happen, how to avoid them, and best practices and tools for reliable PDF-to-PDF workflows — whether you’re compressing files, merging documents, converting PDFs to different PDF versions, or re-exporting after edits.

Why formatting changes occur

• Fonts not embedded: If a PDF references fonts that aren’t embedded, target systems will substitute them, changing line breaks, spacing, and character shapes.
• Color/profile mismatches: Converting between color spaces (RGB ↔ CMYK) or dropping color profiles can shift appearance, especially for print.
• Transparency and blend modes: Some PDF readers or converters flatten transparency differently, producing visual changes.
• Version incompatibilities: Older PDF viewers or export targets may not support newer features (layers, annotations, forms, advanced typography).
• Compression and downsampling: Re-saving with aggressive image compression or downsampling reduces visual fidelity.
• Incorrect export settings: Tools may rasterize vectors, discard metadata, or alter page boxes (crop/trim/bleed) during export.
• Corrupted object streams or bad optimization: Optimizers can mistakenly remove objects that appear unused but are referenced.

Core principles to preserve formatting

• Embed fonts whenever possible. Embedded fonts travel with the file and prevent substitutions.
• Keep color profiles intact or intentionally convert using correct rendering intents.
• Avoid unnecessary rasterization — keep vector artwork as vectors.
• Use a non-destructive workflow: make edits on a copy; keep an original unchanged.
• Choose the correct PDF version for your target (e.g., PDF/A for archiving, PDF/X for print).
• Verify page boxes (media, crop, trim, bleed) and maintain source dimensions.
• Test on the intended target systems (software/printer) before finalizing.

Preparing the source PDF

1. Inspect fonts and resources

   • Use a PDF inspector (Adobe Acrobat Preflight, PDFtk, Ghostscript, or other PDF utilities) to list embedded vs. referenced fonts.
   • If fonts aren’t embedded, obtain and embed them, or convert text to outlines only if editing won’t be needed later.

2. Check color and images

   • Identify the color space of images and artwork. For print, convert images to CMYK using the correct ICC profiles; for screen, prefer sRGB.
   • Check image resolution: keep 300 ppi for print photos, 150–200 ppi may be acceptable for less critical print; 72–150 ppi for screen-only documents.

3. Review transparency and layers

   • Flatten transparencies carefully if the target or printer requires it, but keep an unflattened master for future edits.
   • Preserve layers if you anticipate needing them later; some workflows require merging layers for compatibility.

4. Confirm page boxes and orientation

   • Make sure media, crop, trim, and bleed boxes are set correctly and consistently across pages.

Tools and workflows that maintain formatting

• Adobe Acrobat Pro

  • Use Preflight to analyze and fix fonts, color, transparency, and PDF/X or PDF/A compliance.
  • When saving, choose “Retain existing” for image and font settings if you only need minor metadata changes.
  • Use “Reduce File Size” cautiously; customize downsampling and compression settings.

• Affinity Publisher / Designer

  • Export settings allow control of font embedding, color profiles, and image compression. Good for graphic-heavy PDFs.

• PDF editors (e.g., PDF-XChange, Foxit PhantomPDF)

  • Provide font embedding and export options; varying levels of Preflight capability.

• Command-line tools (Ghostscript, qpdf, mutool)

  • Ghostscript:
    • Useful for reconciling versions and optimizing, but default settings may downsample images. Use explicit parameters to preserve image quality and fonts.
  • qpdf:
    • Good for linearization, encryption, and structural transformations without re-rendering content.
  • mutool (from MuPDF):
    • Useful for inspecting objects and extracting resources; less likely to alter rendering when used for manipulation.

• PDF library workflows (Java/PDFBox, iText, PyPDF2 / pikepdf)

  • Programmatic editing can preserve underlying objects when done carefully (e.g., manipulating annotations or metadata without re-creating pages).
  • Beware: some libraries rebuild content streams and may inadvertently rasterize or alter font references.

Common tasks and how to do them safely

• Merging PDFs

  • Use tools that copy page objects without re-rendering (qpdf, iText, pikepdf). This preserves fonts and images.
  • After merging, verify combined page boxes, bookmarks, and outline metadata.

• Compressing PDFs

  • Prefer JPEG2000 or appropriate JPEG quality levels; avoid aggressive downsampling for images you need to keep sharp.
  • Remove unused resources and metadata, but don’t strip font embedding unless fonts are already embedded in multiple documents and inflate size unnecessarily.
  • Use linearization for faster web viewing without altering quality.

• Converting PDF versions (e.g., to PDF/A)

  • Use a Preflight/validation tool with an explicit conversion profile. PDF/A requires fonts to be embedded and disallows encryption, so plan accordingly.
  • Validate the conversion with a PDF/A viewer or validator.

• Re-exporting after editing

  • Save an archival master (original) and export a working copy.
  • When exporting, explicitly set font embedding to “embed all fonts” or “subset” depending on needs.
  • Preserve color profiles and choose “Do not downsample” or set thresholds above your image resolutions.

• OCR and searchable PDFs

  • Keep the original image layer and store OCR text as a separate invisible text layer rather than replacing images.
  • Use OCR engines that preserve layout (ABBYY FineReader, Adobe Acrobat OCR) and verify language and dictionary settings.

Practical export settings (recommended values)

• Fonts: Embed all fonts; subset if file size is a concern but be aware subsetted fonts can’t be edited easily.
• Images: No downsampling for archival; if needed, downsample to 300 ppi for print, 150 ppi for screen-only distribution.
• Compression: Use lossless (ZIP) for graphics or high-quality JPEG/JPEG2000 for photos at 8–12 quality (JPEG scale).
• Color profiles: Keep source ICC profiles or convert with the correct intent (perceptual/relative colorimetric as appropriate).
• PDF version: Match the target’s required features — PDF/A-1b for long-term archival, PDF/X-1a/3 for print production, PDF 1.7+ for advanced transparency and layers.

Troubleshooting common problems

• Text reflow/spacing changes
  • Cause: font substitution. Fix: embed fonts or convert text to outlines (last resort).
• Blurry images after export
  • Cause: downsampling or recompression. Fix: increase image resolution or lower compression.
• Missing annotations/forms
  • Cause: export settings that flatten or omit interactive objects. Fix: enable annotations/forms in export or flatten intentionally and keep a copy.
• Color shifts when printing
  • Cause: incorrect color profile or missing CMYK conversion. Fix: convert images to the printer’s CMYK profile and preserve black composition for text.
• Large file sizes after merging
  • Cause: duplicate embedded fonts or unoptimized images. Fix: subset fonts, optimize images, remove unused objects, or use a deduplication-enabled tool.

Sample quick workflows

• Fast, safe merge (preserve everything)

  • Use qpdf or pikepdf to concatenate pages without re-rendering:
    • Command-line: qpdf –empty –pages file1.pdf file2.pdf – out.pdf
  • Validate in a viewer to ensure fonts are intact.

• Compress for web viewing (small & readable)

  • Make a working copy.
  • Downsample images to 150 ppi, compress photos with high-quality JPEG.
  • Subset fonts and linearize the PDF for fast web streaming.

• Prepare for print (high fidelity)

  • Convert images to CMYK with printer ICC profile.
  • Embed all fonts (no subsetting).
  • Export as PDF/X-1a or PDF/X-4 depending on printer specs.
  • Run preflight and fix any transparency or overprint issues.

Checklist before finalizing

• Fonts embedded or a documented reason for not embedding.
• Color profiles set or intentionally converted.
• Images at adequate resolution and appropriate compression.
• PDF version and compliance match target requirements.
• Annotations, forms, and layers handled as needed.
• A validated copy opens correctly in at least two different readers (Adobe Acrobat and an alternate).
• Keep the original master file.

Preserving formatting when converting or re-exporting PDFs is mainly about controlling resources (fonts, color, images) and using non-destructive tools and settings. With a consistent workflow, checks, and the right export choices, you can reliably move from PDF to PDF without surprises.