When Google's crawlers index a website, they will only be able to recognize the existence of pages that the website's other pages internally link to because the crawlers proceed by following every link they come across. A sitemap posted within the website's hosting domain can help ensure that all of a website's relevant URLs will not remain orphaned in this manner. PDF files that are hosted on websites may be counted as standard web pages for all intents and purposes so long as they are internally linked to in the same manner. However, presumably since PDF files are not expected to have their contents changed by the website's owner as routinely as the site's main content, it may take longer for the crawlers to refresh a PDF file's rankings in SERPs.
Even so, those who lack knowledge related to PDFs may find that Google's crawlers will never include it in the expected SERPs regardless of how much time is allotted. Like what can happen with regular pages of web content, the only available links to the PDF may not be open for crawlers to follow, which can happen if they have the "nofollow" element. Additionally, the site's native "robots.txt" file may be instructing crawlers to disavow the location in which the PDF is stored. On platforms like WordPress, it is likely that a PDF would be stored in a disorganized file folder dedicated to file uploads that is not indexed by default.
A PDF file's contents are also as susceptible as any standard web page's contents to being regarded as weak content in terms of SERP positions, so standard SEO techniques must be applied to make the PDF noticeable in SERPs. Primarily, the PDF's content should include keywords that are not overly competitive yet come across as highly relevant to the industry the website itself covers. Among the technical elements that PDF files must exclusively deal with, however, are a need for the page hosting a PDF to be well-optimized for search engines in its own right and a need for the PDF not to be an encrypted file. For more information click here https://www.reddit.com/r/SEO/comments/c9ccf6/madeapdfuploadedittowordpressandlinked_to/.