ChatGPT Cites PDFs in 5.7% of Its Sources vs 0.32% for Google AI Overviews

    5.7% of the sources ChatGPT cites are PDF documents, against 0.32% for Google AI Overviews and 0.42% for Google AI Mode. Across five AI engines, 1.5% of citations are documents rather than web pages, and 57% of the PDFs cited come from government, university or military websites.

    Citations that are documents by AI engine
    ChatGPT
    5.7%
    Perplexity
    1.62%
    Gemini
    0.57%
    Google AI Mode
    0.42%
    Google AI Overviews
    0.32%
    All five engines
    1.51%

    Source: Suff Digital analysis of 155,312 cited URLs · answers from ChatGPT, Gemini, Perplexity and Google's AI features, September 2026

    Cited PDFs by website
    consumerfinance.gov
    86
    noaa.gov
    78
    usda.gov
    69
    naic.org
    55
    medicare.gov
    53
    irs.gov
    52
    nih.gov
    51
    wisc.edu
    37
    cdc.gov
    35
    fda.gov
    32
    energy.gov
    29
    who.int
    27

    Source: Suff Digital analysis of 155,312 cited URLs · answers from ChatGPT, Gemini, Perplexity and Google's AI features, September 2026

    Source: ChatGPT Cites PDFs in 5.7% of Its Sources vs 0.32% for Google AI Overviews - Suff Digital