Elements Of Partial Differential Equations By Ian Sneddonpdf Link -

Looking up on Google, "Elements of Partial Differential Equations Ian Sneddon PDF" – the first result is a link to Google Drive, but that's a third-party site and might not be reliable. Another result is from Archive.org, which is a reputable source. Let me check the ISBN. The ISBN for the 1950 edition is 0-07-082255-5. If the book is public domain, Project Gutenberg might have it.