Welcome to Inkscape Community!
When you say you're completing a PDF form, it sounds like you mean you're "filling in the blanks". Is that correct? When I first read your message, I thought you were creating a PDF form that had been originally started in some other program, and you wanted to finish creating it in Inkscape. But now I think you mean you're filling in the blanks. Yes? No?
Is there any particular reason why you're using Inkscape for this? It seems like some text editor or desktop publishing program would be better suited for that. Or even a browser might be better for filling it out. For creating it, I think you'd have to use Adobe Acrobat.
Inkscape is primarily a graphics program. Yes, it has a Text tool, but it's not really a text editor. Inkscape's text features are nowhere close to something like Libre Office or Word, for example. Even this message editor in this forum is more sophisticated than Inkscape's text capability!
Well actually, the answer is probably the same either way (creating the form or filling out the form), as far as I understand. While Inkscape is capable of editing certain PDF content (usually only vector content), and creating PDF files and converting SVG to PDF, Inkscape is an entirely different program from Adobe Acrobat (or whatever program created the form).
Inkscape is a graphics program and it's text features are nowhere near comparable to something like Libre Office or Open Office or Word, or etc.
I did some searching, out of curiosity, because I've never seen this question asked about Inkscape before. I found this, which looks pretty interesting. Maybe it can help you?
https://www.pdfescape.com Or otherwise, if you have some reason for wanting to use Inkscape for this, please give us some more details about exactly what you're doing and why. Maybe we can help you figure something out. Also, please attach the SVG or PDF file, so we can see exactly what's there.
