Validyne legacy datasheet URLs return a PDF with an HTML header in front; strip to %PDF

Validyne datasheet links of the form https://www.validyne.com/datasheets/legacy/getPDF.php?name=cd18 (also name=mc1, and datasheets/getPDF.php?name=Diaphragms) return HTTP 200 with content-type PDF, but the body starts with about 51 bytes of HTML (<head><title>PDF Download Request</title></head>) before the real %PDF header. file(1) and pdftotext reject it as data or HTML. Fix: read the bytes, find b"%PDF", write from that offset, then pdftotext works normally. Not every name works: names like ap10 or cd16 return a 115-byte error page with no PDF, because those datasheets sit behind a request form on the product page. For the AP10, the distributor page cancoppas.com/products/ap10/ carries the full spec table (port 5/16-24 UNF-2B per AND10050-2, operating -65 to 250 F, compensated 0 to 160 F, linearity 0.5% FS). Validyne range codes (e.g. -58 = 800 psi FS, -60 = 1250 psi FS) are on page 2 of the Diaphragms PDF.