What the problem actually is
A PDF doesn't always contain the real font used for the text: it can just reference its name. If the font isn't embedded in the file and isn't installed on the system opening it — or on the printing device — it gets automatically substituted with a similar font. This changes the text's proportions, line spacing, and sometimes the entire layout.
Three different things: embedded, substituted, outlined
An embedded font carries the real character data inside the PDF itself: this is the ideal condition, the text stays identical everywhere. A substituted font gets automatically replaced by a similar font present on the system opening the file — often with no visible warning at all. Text converted to outlines becomes a vector shape instead of text: it no longer depends on any font, but loses the ability to be selected, searched or edited as text.
When embedding the font is better than outlining it
If the text needs to stay editable, selectable or accessible (for example for screen readers, document search, later edits), embedding the font is the right choice. Systematically converting everything to outlines isn't a rule to apply always: it should be evaluated case by case, and is warranted only when the specific print workflow explicitly requires it.
Risks of converting to outlines
An outline no longer depends on a font, but very small text or thin strokes can render worse once turned into vector shapes, depending on the printing engine (RIP) processing the file. The conversion is also irreversible: once done, the original text is no longer recoverable as text.
How to check if fonts are embedded
In Adobe Acrobat Pro: File > Document Properties > Fonts tab. The panel lists every font used in the PDF and shows whether it's embedded or only referenced — a direct check, before sending the file, that avoids surprises at the print stage.
Common mistakes to avoid
Assuming a font installed on your own computer will also be available elsewhere. Ignoring font-not-embedded warnings when exporting the PDF. Sharing files between collaborators with different versions of the same font (even small differences can alter the layout). Using a font without checking its license allows embedding in a PDF intended for print.