What Markdown is
A Markdown table is rows of pipe-separated cells with a dashed rule under the header. Alignment is set by placing colons in that rule.
README files, GitHub issues, documentation sites, Obsidian and Notion.
What PDF is
PDF describes a page: glyphs at coordinates, not rows and columns. A table in a PDF is a visual arrangement, not a data structure.
Reports, invoices, statements and anything sent to be read rather than processed.
What changes when you convert Markdown to PDF
Leading and trailing pipes are optional and both are handled. A pipe the author escaped with a backslash is read as data rather than a column break, which is the usual reason a hand-written table parses one column too wide.
The table is drawn into a paginated document with the header repeated on every page, so a long table stays readable past page one. Page size, orientation and font size are all adjustable.
What carries over from Markdown to PDF
Markdown records 2 things about a table that PDF has no way to hold.
Nothing in PDF records that the first row is a header. It is drawn at the top and looks like one, which is all that is left of the distinction.
PDF is the end of the line for this data. Reading the table back out of it is a separate and much harder problem than writing it, so keep the Markdown if you will need the values again.