10 Common PDF Conversion Mistakes That Ruin Your Documents

PDF conversion looks like a solved problem, right? Every OS, every browser, every office suite claims to "export PDF." Then you submit a contract, and the other side's copy renders your typography in Courier New. Or you export a 12-page slide deck to images and the photos look like they were faxed. Most of these disasters are not random — they are the same ten mistakes, made in the same order, over and over. I've catalogued the ones I see weekly, with the cause and the fix for each.

1. Fonts get swapped for ugly defaults

What happens: your carefully typeset resume or proposal opens on the recipient's machine in some generic serif — or worse, a serif that doesn't have the ligatures and special characters you used, so "é" becomes "?" and kerning collapses.

Why: PDFs don't always embed fonts by default. If the font isn't embedded and the reader's device doesn't have it, the viewer substitutes a fallback. This is especially common with Google Fonts, display fonts, and anything exported from a browser or a design tool without "embed fonts" checked.

Fix: always export with fonts embedded (in Word: File → Options → Save → "Embed fonts in the file"; in print-to-PDF dialogs look for "embed all fonts"). If you're going from images to PDF instead of from text, this problem vanishes entirely — text becomes pixels, so nothing can be substituted.

2. Images come out blurry

What happens: photos in your PDF look soft, pixelated when zoomed, or like JPEG artifacts. The source image was crisp; the PDF is muddy.

Why: two causes. Either the export downsampled embedded images to 72 or 96 DPI (web resolution — fine on screen, terrible on paper), or you placed a small web-resolution image (say 800 px wide) and stretched it to fill a full page. Also see mistake 9 for the reverse problem.

Fix: set image quality to "high" or 300 DPI in the export dialog, and never upscale small images. When you're going the other direction — PDF pages back to images — pick DPI deliberately: 150 for screen reading, 300 if anyone will print the result. Our PDF to JPG converter exposes that DPI choice instead of hiding it at 96.

3. Margins and layout shift

What happens: the PDF that looked perfect in your app now has content cut off at the page edge, gigantic empty margins, or two pages worth of text squeezed onto one.

Why: "A4" and "Letter" are different physical sizes — A4 is 210×297 mm, US Letter is 216×279 mm. Cross-continent exports routinely reflow text because the paper size silently changed. The other cause is fitting content "to width" with no margin setting, so images bleed to the edge.

Fix: state the paper size explicitly and preview the first page before exporting the whole batch. When you're assembling photos into a PDF, set the margin slider deliberately (8–15 mm looks normal; 0 looks like a broken print) and keep "fit to width" on so nothing overflows.

4. Pages are rotated the wrong way

What happens: landscape photos end up sideways in the PDF, or portrait scans print upside-down. Recipients rotate their heads for a second, then mentally file your document as unprofessional.

Why: JPEG orientation is often stored in EXIF metadata (the "Orientation" tag) rather than applied to the actual pixels. Many PDF assemblers ignore that tag and bake the raw pixel orientation into the page. A photo your phone took "upright" can land in the PDF rotated 90 degrees.

Fix: preview the first page (or the first few) before downloading — the tool on this site renders a live first-page preview precisely for this. If pages come out mixed, re-export with the orientation set explicitly in the tool instead of letting it guess.

5. Transparent backgrounds turn solid black

What happens: you place a logo with a transparent background onto a white page, export, and the logo's transparent areas are now a black rectangle.

Why: JPEG does not support transparency at all. Any conversion path that flattens to JPEG must fill transparency with something — and if the tool's default fill is black (or none, rendered as black by the viewer), you get the ink blotch. This is the classic PNG-to-PDF-then-back bug.

Fix: when converting PNG with transparency to JPG or embedding in a JPEG-based PDF, explicitly set the background fill to white (or brand color). Our format converter shows a "transparent background will be filled" warning and lets you pick the fill color before you convert.

6. Encrypted or password-locked PDFs

What happens: your conversion tool returns "this PDF is password protected" or "permission denied," and the exported pages are blank or encrypted too.

Why: PDFs carry permission flags — even if you can open and read them, the author may have disabled content extraction, printing or modification. Conversion tools respect (or crash into) those flags. Sometimes the file is also encrypted at open, which is a different problem.

Fix: you can't strip DRM you're not authorized to strip — if it's your own document and you forgot the password, recover it from whoever issued the PDF. For documents you created, disable encryption before converting. Never feed a locked PDF into an online "unlock" service — that uploads your confidential file to an unknown server.

7. A scanned page treated as a text PDF

What happens: the PDF looks fine visually, but you can't select or copy any text, search doesn't work, and screen readers read it as nothing.

Why: a phone scan is just a photograph glued onto a page. That's an image-based PDF, not a text PDF. People call this "flattening" and it's correct for some purposes (signatures, legal looks), wrong for others (accessible documents, searchable archives).

Fix: decide upfront what the PDF is for. A scanned receipt for your records? Image-based PDF is fine. A tender document sent to the public? It needs OCR to be searchable and accessible. Build the PDF with that in mind — when you merge photos into a PDF, you're intentionally making the first kind; if you need the second, plan an OCR step separately.

8. Special characters in filenames

What happens: the batch download ZIP arrives and half the files are named ____.jpg, or a tool refuses a file called Receipt #2 (Final v2).pdf.

Why: file systems and HTTP encodings disagree on #, ?, &, %, quotes and emoji. Server-side conversion pipelines sometimes sanitize them aggressively, and older ZIP creators mangle non-ASCII names. It's a small thing, until your 20-file batch arrives unlabeled.

Fix: rename source files to plain ASCII before batch converting: letters, numbers, hyphens, underscores. Keep version markers in the name, not parentheses and emoji. Local browser tools sidestep most of this because the files never go through a server, but the habit still pays off.

9. Output files that are unnecessarily enormous

What happens: a 10-page PDF ends up at 47 MB. Email bounces. The upload form rejects it. Nobody reads a 47 MB attachment.

Why: either the source PDF embeds full-resolution images (a 40 MB scan at 600 DPI), or the conversion re-encoded everything at quality 100. PDF-to-image exports at 300 DPI for a 50-page document routinely produce 30 MB ZIPs — that's correct for print, overkill for email.

Fix: match DPI to the destination: 72–96 for on-screen previews, 150 for email and forms, 300 only for print. A 150 DPI export of the same 50 pages is a tenth the size. If you're assembling images into a PDF, start from reasonably-sized images (1600 px on the long edge) rather than full camera exports.

10. Forgetting to actually check the result

What happens: you send the PDF off and find out — from the recipient — that pages are missing, the cover image is sideways, or the footer says "DRAFT" on every page.

Why: conversion tools are optimistic. They report success when the file was produced, not when it's correct. The last 2% of any conversion pipeline is manual inspection, and it's the step everyone skips.

Fix: the 60-second habit: open the output, check page count against input, flip to the first, middle and last page, and zoom once. On a phone, open it there too — mobile PDF renderers differ from desktop. Thirty seconds of checking catches 90% of the mistakes above.

Frequently asked questions

Why does my PDF look fine on my screen but wrong on someone else's?

The two most common reasons are missing embedded fonts and A4-vs-Letter size differences. Your machine has the fonts; theirs doesn't. Your paper size may differ from theirs, causing text reflow. Always embed fonts and set the paper size explicitly when exporting.

What DPI should I export PDF pages at?

72–96 DPI for quick on-screen previews, 150 DPI for email and upload forms, 300 DPI only if the images will be printed. Exporting at 300 DPI for screen use produces files 4–10× larger for no visible benefit.

Can I convert a password-protected PDF?

Only if you have the password and the permissions allow extraction. If it's your own document, remove the password in the security settings first. Avoid online "unlock PDFs" services — they require uploading confidential documents to unknown servers.

Why do my PNG logos turn black in the PDF?

Because the conversion flattened transparency onto a default black background. JPEG-based pipelines cannot keep transparency — always choose an explicit white or brand-color fill when exporting PNGs with transparent backgrounds to JPG/PDF.

How do I check a converted PDF before sending it?

Open it and verify: page count matches the source, first/middle/last pages render correctly, text is selectable where it should be, and it opens on a phone. Sixty seconds of review catches nearly every conversion error.

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