How PDF Text Extraction Works on CompareStack
Selectable text, then a line diff
PDF Compare parses each file and reads its text layer. That string is not a picture of the page. A change that only moves a logo, a stamp, or a font will not appear unless the extracted words change.
Before alignment, the extractor output is normalized: carriage returns become line feeds, repeated spaces collapse, and single line breaks inside a paragraph are joined. The paragraph is then split on sentence-ending punctuation. The diff runs on those lines, using the same added, removed, and changed markers as Text Compare.
What fails or looks empty
Image-only scans have little or no text layer. This tool does not OCR them. If you cannot select a sentence in a PDF reader, PDF Compare will not invent one.
Encrypted or damaged files fail extraction. You will see a short failure message rather than the parser’s internal error. Headers, footers, and page numbers that are part of the text layer can still show up as repeated changes.
When to use a different tool
If you already copied the paragraphs out, Text Compare avoids the extraction step. If the source is still DOCX, Word Compare reads the document text instead of a PDF text layer. Neither path is a visual proof.