Directed search · Controlled vocabulary
Count your search terms
and build the VOSviewer network
You define the keywords; the app counts the occurrences and co-occurrences across your PDFs and generates a JSON file ready for VOSviewer Online. With grouped synonyms, compound terms, wildcards and thematic categories.
1 — Upload PDFs
Drag PDFs here
or click to select — multiple files supported
2 — Search terms (controlled vocabulary)
Type one term per line. Just what you want to search for.
Each word with the variants that will actually be counted. This is your study's thesaurus.
The app is subject-neutral. Load a domain pack (a .txt library for your topic) so that bare terms expand to their variants; the same .txt format works as both a term list and a library. In area A you can also group synonyms manually with =, set a category in [ ] and use a wildcard with *. Manual lines always take priority over the library.
3 — Network parameters
Terms co-occur if they appear in the same PDF (binary, the bibliometric standard)
Minimum for a term to enter the network
Minimum link strength between two terms
How to use
Upload the PDFs
Drag or select one or more PDFs. The text is extracted locally, with nothing sent to a server.
Define the terms
List your keywords, group synonyms with "=", use "*" for variations and "[ ]" for thematic categories.
Open in VOSviewer
Download the generated JSON and open it in VOSviewer Online. Node colours follow your categories.
Frequently asked questions
How does this differ from PDFWords?
PDFWords extracts every word from the PDFs automatically (an open, exploratory approach). PDFTerms does the opposite: you control the vocabulary, listing exactly the terms of interest. This is the directed approach, well suited to systematic reviews and to testing predefined concepts.
How do I group synonyms?
Use the equals sign. Example: CO2 = carbon dioxide; dióxido de carbono. All the variants are counted as a single term, with the label to the left of "=". Separate the variants with a semicolon or comma. You can also let the app generate the synonyms automatically from the library.
How do I use wildcards and compound terms?
The * captures variations: emission* matches emission, emissions, emitting. Compound terms work directly: shore power searches for the whole phrase. The search ignores case and accents.
What is binary counting per document?
In the "Document" scope, two terms co-occur if they appear in the same PDF, counted once per document. This prevents a long PDF that repeats a term many times from dominating the network. It is the recommended bibliometric standard. In the "Sentence" scope, co-occurrence is counted for every sentence in which the two terms appear together.
How do categories appear in VOSviewer?
Each category in [ ] becomes a cluster in the JSON, and VOSviewer assigns a distinct colour to each cluster automatically. Terms without a category fall into a neutral group.
Some terms were not found — what now?
The result lists the terms with zero occurrences, for quality control. Check the spelling and accents, try a wildcard (e.g. govern*) or add synonyms. Scanned PDFs (image only) require OCR first.